tests: skip time consuming mock builds for code-only changes

tests/basic/rpm.t takes a bulk of the time for the regression tests.
Often the building of the rpm is not affected at all and therefor the
tests does not add any value.

With this change the rpmbuild/mock test will only be run when some
changes affect the build system. Changes affecting 'tests/', 'doc/',
'*.py', *.c' and '*.h' do not trigger the test anymore.

Change-Id: Ic188b9e26cde3113b2bdf9cd1fab56d9fd85a4b7
BUG: 904005
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-on: http://review.gluster.org/4429
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>