add support for commit message in release

[cirulls]

I added support for a commit message when finishing a release. My git setup forces me to provide a commit message when finishing a release (I believe this is not unusual in many git configurations) so I added a message parameter. As documented, this option is used only with the command 'release' action 'finish'. The default value is " " (which I admit is not very elegant), unfortunately the empty string would break compatibility when no message is passed. The format of the command is:

git flow release finish -m"{message}" {name}

This is in line with what suggested in nvie/gitflow#50

I added your GitHub ID as recommended in the ansible's module checklist and I dared to add mine as contributor.

[jdinunzio]

Thank you very much, Sandro!

Pull request merged.

[cirulls]

Thanks, that was very quick! I added my comments on your module at ansible#372. Thanks for sharing this useful module, it made my work easier!