gradle: Include Project.isNoBundles() in release task enabled expression

Only release a project if -nobundles is not set.

Fixes https://github.com/bndtools/bnd/issues/592

Signed-off-by: BJ Hargrave <bj@bjhargrave.com>
Merge pull request #594 from bjhargrave/issue592

gradle: Include Project.isNoBundles() in release task enabled expression