Allow for default coordination mechanism

[oweidner]

Especially with BigJob deployment on XSEDE and the fact that we decided to move to Redis, it doesn't make too much sense to have the user explicitly define the URL every single time:

COORDINATION_URL = "redis://password@hostname:6379"
bj = bigjob(COORDINATION_URL)

since it will always be the same for a given deployment. I propose to add an option to setup.py that allows to set a default URL for BigJob coordination, e.g., BIGJOB_DEFAULT_COORDINATION=redis://quary... easy_install BigJob, similar to what I do with the connection setting in bigjob-server: https://github.com/oweidner/bigjob-server/wiki/Installation.

Subsequently, the user can leave the coordination_url in the BigJob constructor blank and/or use a predefined variable, i.e.,

bj = bigjob()

or

bj = bigjob(bigjob.DEFAULT_COORD)

One could think about the same for the pilot-job LRMS, e.g.,

bj.start_pilot_job(bigjob.DEFAULT_RM,  (instead of having to remember e.g., gram://lonestar...whatever)

I think being able to define optional default options for machine-specific deployments would make BigJob more user-friendly.

[pradeepmantha]

I think specifying COORDINATION_URL as environment variable will help to adjust coordination system dynamically. Since this will avoid re-installing of BigJob, if COORDINATION URL need to be changed.

[oleweidner]

config file / environment variable support for redis connection parameters would still be useful, IMHO. Maybe it would also prevent people from putting plain-text passwords in their code...

[oleweidner]

Don't think that has any relevance anymore.