Add branching to git

[mwitkow]

This allows users to customize the ref to use from the branch. For example:

  "vcs": "git",
  "vcs-config": {
    "ref": "releases/9.0"
},

[igorwwwwwwwwwwwwwwwwwwww]

Yes please!

[kylej-ibm]

Please merge this feature

[derimagia]

url-pattern config option should get {ref} option and the default option should use this:

https://github.com/improbable-io/hound/blob/c6c5459ffb60207e13c0d8cfaab2e7eed8658108/config/config.go#L16

[sbergot]

@derimagia this would be a nice addition, but right now this you can still do this by hardcoding the reference in the url-pattern.

[frankchdez]

@mwitkow consider adding "--branch", g.Ref, to the Clone method

[dmsimard]

#275 provides the ability to specify a git branch other than the hardcoded "master" and it works for us.