Add option to install apps using git

[mhemesath]

It would be useful for development to be able to install apps using Git. Something such as:

Installing from ref

    "TA-example_app": {
      "download": {
        "git" : "http://github.com/cerner/splunk_app",
        "ref": "4dad",
        "version" : "1.0"
      }
    }

Installing from branch

    "TA-example_app": {
      "download": {
        "git" : "http://github.com/cerner/splunk_app",
        "branch": "master",
        "version" : "1.0"
      }
    }

Installing from tag

    "TA-example_app": {
      "download": {
        "git" : "http://github.com/cerner/splunk_app",
        "tag": "v1.0",
        "version" : "1.0"
      }
    }

[ben-roling]

+1 to this idea -- I was just mentioning to @acharlieh a desire for the same thing. Specifically I am most interested in the idea of installing from a branch with some concept of an automated refresh interval such that if I push to the branch the changes will automatically be picked up relatively quickly without need to run chef-client again or push a new version of the chef config.