issue #68, support for specifying git branches

[jonpugh]

Excellent, this is exactly what I was thinking.

There are a few changes I'd like to make before merging this:

• [ ] Let's prevent spaces and special characters in environment names. It just causes headaches since we use the environment name in so many places, let's force them to be numbers and letters only when they are created.
• [ ] Change "branch" option to "version". This way you can specify a tag for the environment as well as a branch.
• [ ] Does git ls-remote tell you the default branch? Instead of asking "Do you want to specify a specific repo branch" let's simply ask Version? [master] where "master" is the default branch. We'd have to run git ls-remote before we ask, but I think this is a good place to check for access to the repo.

[badri]

Thanks for the comments :+1: I thought naming "branch" to "version" would be a bit misleading, as we really mean git branches when we say branch. That's anyways my opinion. What do you think?

Also, I couldn't find a way to get the default branch of a repo without cloning it. That's why I had it as a two-fold step, to ask for a specific branch and if answered yes, clone it. Otherwise, it is going to clone the default branch anyways.

[badri]

Output of environment name checking:

$ terra environment:add
Which app? 
  [d7    ] d7
  [kalvi ] kalvi
 > kalvi
Environment name? foo-bar
 ERROR  Environment foo-bar cannot contain spaces or special characters.
Environment name? foo%bar
 ERROR  Environment foo%bar cannot contain spaces or special characters.
Environment name? foo bar     
 ERROR  Environment foo bar cannot contain spaces or special characters.
Environment name? foobar
Path: (/home/lakshmi/Apps/kalvi/foobar) 

Output of "branch" feature in env add:

$ terra environment:add
Which app? 
  [d7    ] d7
  [kalvi ] kalvi
 > kalvi
Environment name? foo
Path: (/home/lakshmi/Apps/kalvi/foo) 
Getting the default branch for badri@git.drupal.org:project/kalvi.git 
Version? [7.x-1.x]
Checking if branch 7.x-1.x exists in badri@git.drupal.org:project/kalvi.git 
Cloning into '/home/lakshmi/Apps/kalvi/foo'...
* 7.x-1.x
On branch 7.x-1.x
Your branch is up-to-date with 'origin/7.x-1.x'.

nothing to commit, working directory clean
Environment saved to registry.

[jonpugh]

Thanks @badri!! I've merged this work, with some commits afterwards for cleanup.

I've removed the logic for asking for branch and checking if it's valid. I appreciate the work, but I think it adds unnecessary complexity to this code.

Instead, use the option "--ref" if you want to create an environment with a specific branch, tag, or sha.

If you don't use the option, we just assume you want the default branch.

if you specify a ref that does not exist, we just ignore it and use the default branch.

Thanks a ton for this effort! Keep it coming! :+1: