Require "-b" for each backend parameter given to "reproman create"

[chaselgrove]

This makes more sense to me, especially with the environment name being a naked command line argument (without a flag) -- which arguably belongs at the end of the command line -- but this isn't possible if -b slurps up everything following it.

[codecov[bot]]

Codecov Report

Merging #534 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #534   +/-   ##
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  Coverage   89.75%   89.75%           
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  Files         148      148           
  Lines       12483    12483           
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  Hits        11204    11204           
  Misses       1279     1279           

Impacted Files	Coverage Δ
reproman/interface/create.py	94.11% <ø> (ø)

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[yarikoptic]

Note that

• -- could be used to separate options from positional args, e.g.

  $> reproman create -t ssh -b host=localhost port=22 -- newlocalhost   
  2020-07-02 18:07:17,928 [INFO   ] Created the environment newlocalhost 

  so alternatively we could have just fixed up documentation for create to make it more obvious

• with some bids-apps in mind I started to more often list OPTIONS after positional arguments (e.g. here would be reproman create NAME -b ...) to mitigate this:

  $> reproman create newlocalhost2 -t ssh -b host=localhost port=22              
  2020-07-02 18:09:07,508 [INFO   ] Created the environment newlocalhost2 

  but

  it seems to be the only option (not positional) of this kind

$> git grep -B10 'nargs=.[\+\*]' | grep -e 'Parameter' -e args          
reproman/interface/backend_parameters.py-class BackendParameters(Interface):
reproman/interface/backend_parameters.py-        backends=Parameter(
reproman/interface/backend_parameters.py-            args=("backends",),
reproman/interface/backend_parameters.py:            nargs="*")
reproman/interface/create.py-        # specs=Parameter(
reproman/interface/create.py-        #     args=("-s", "--spec",),
reproman/interface/create.py:        #     # nargs="+",
reproman/interface/create.py-        resource_type=Parameter(
reproman/interface/create.py-            args=("-t", "--resource-type"),
reproman/interface/create.py-        # only_env=Parameter(
reproman/interface/create.py-        #     args=("--only-env",),
reproman/interface/create.py:        #     nargs="+",
reproman/interface/create.py-        # existing=Parameter(
reproman/interface/create.py-        #     args=("-e", "--existing"),
reproman/interface/create.py-        backend_parameters=Parameter(
reproman/interface/create.py-            args=("-b", "--backend-parameters"),
reproman/interface/create.py:            nargs="+",
reproman/interface/execute.py-        command=Parameter(
reproman/interface/execute.py-        args=Parameter(
reproman/interface/execute.py-            doc="list of positional and keyword args to pass to the command",
reproman/interface/execute.py:            nargs="*",
reproman/interface/install.py-        spec=Parameter(
reproman/interface/install.py-            args=("spec",),
reproman/interface/install.py:            nargs="+",
reproman/interface/jobs.py-        queries=Parameter(
reproman/interface/jobs.py:            nargs="*",
reproman/interface/ls.py-        refresh=Parameter(
reproman/interface/ls.py-            args=("-r", "--refresh",),
reproman/interface/ls.py-        resrefs=Parameter(
reproman/interface/ls.py-            args=("resrefs",),
reproman/interface/ls.py:            nargs="*",
reproman/interface/retrace.py-        spec=Parameter(
reproman/interface/retrace.py-            args=("--spec",),
reproman/interface/retrace.py:            # nargs="+",
reproman/interface/retrace.py-        path=Parameter(
reproman/interface/retrace.py-            args=("path",),
reproman/interface/retrace.py:            nargs="*",

so sounds like it is a single point of such cmdline UI pattern.

And @kyleam used the same "append" pattern in `run`

```shell $> git grep -B10 'action.*append'| grep -e 'Parameter' -e args -e append reproman/cmdline/main.py: '-C', action='append', dest='change_path', metavar='PATH', reproman/cmdline/main.py: "-c", "--config", metavar="CONFIG", action="append", reproman/interface/run.py- batch_spec=Parameter( reproman/interface/run.py- args=("--batch-spec", "--bs"), reproman/interface/run.py- batch_parameters=Parameter( reproman/interface/run.py- args=("--batch-parameter", "--bp"), reproman/interface/run.py: action="append", reproman/interface/run.py- job_specs=Parameter( reproman/interface/run.py- args=("--job-spec", "--js"), reproman/interface/run.py: action="append", reproman/interface/run.py- job_parameters=Parameter( reproman/interface/run.py- args=("--job-parameter", "--jp"), reproman/interface/run.py- # TODO: Use nargs=+ like create's --backend-parameters? I'd rather reproman/interface/run.py- # use 'append' there. reproman/interface/run.py: action="append", reproman/interface/run.py- inputs=Parameter( reproman/interface/run.py- args=("-i", "--input"), reproman/interface/run.py: action="append", reproman/interface/run.py- outputs=Parameter( reproman/interface/run.py- args=("-o", "--output"), reproman/interface/run.py: action="append", ```

So it would make cmdline UI more consistent. Thus Merging, thanks!