Merge pull request #87 from sbesson/integration_test_refactor

Refactor the TestRebase integration test
Do not create PR comment when outside Jenkins environment
Move reset and token arguments to the GitRepoCommand

Both set of options are required to initialize the repository using the
init_main_repo() method. Also remove duplicate option definitions in concrete implementations of this class.
Add tag-release command to recursively tag a repo and its submodules

From an input release number, this command tags the main git repository and
each of the registered submodules. The release number is prefixed by a tag
prefix read from the last tag (using `git describe`).
Add integration test for testing the new tag-release command
Use https URL for sandbox cloning
Replace hard-coded script list by nosetests (in verbose mode)
Add no-ask option to the merge integration tests
Add user.name and user.email to global config
Handle case where git describe fails - return empty tag prefix
Add push argument to tag-release command
Define global github.token to work with Sandbox tests
Set Strict host checking to no for github.com in Travis CI
merge master -D org -I include -E exclude: PR 89 (Tag release)