Plugin makes build fail in non git project

[alcarraz]

The plugin makes the jar task to depend on createGitRevision task, that fails if this is not a git repository, the build even fails after performing a git init with a NoHeadException.

There are many options for this:

1. Not adding the dependency if the project is not in a git repository, and maybe not creating the task at all.
2. Letting a project property select if we want to run the task.
3. Ignore the git exception if a project property is set.
4. All of the above.

The easier to implement are 2 and 3.

I don't know if there is an easy way of asking jGit about whether the project is in a git repository or not, without using hard coded literals for implementing 1. But also for this we would need to ask git specific questions from the JPOSPlugin class, of course we can relay that to a GitRevisonTask method.

[ar]

Good point and thank you for PR #6

I'd like to explore option 1 in order to avoid having to manually set the ignoreGit property.

If we go with option 2, it's a good opportunity to use plugin properties so that we can configure something like:

jpos {
   ignoreGit = true
}