use a real git.Repo().commit() object

use a real git.Repo().commit() object

as preparation for vdc-bundles-integration scheme:
requirements define to evaluate commit message for different triggers:
* [merge]: integrate all commits of currently committing branch into
           'integration'-branch by using 'rebase'
* [no-test]: package build should not run any tests

according to documentation, http://goo.gl/kS1rB,
* [no-test] will be ignored if [merge] is also given in the commit message
* [no-test] will be ignored for 'integration' branch at all - it must run the
            full set of tests!

we can access the commit message like this:

  >>> curr_commit.message
  <<< u'test commit\n'