tools.check_patch: Use working dir for project checking

Search LICENSE file from the current working dir instead of the
../check_patch.py file directory, which makes it possible to use
one script to check any autotest-like project.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
Merge pull request #1427 from ldoktor/framework

tools.check_patch: Use working dir for project checking