Changes to make the tests run on Mac

Hello people,

  I had to made the following changes to be able to run the tests on Mac, basically the changes are below

- The check for the leap_tests folder cannot use the whole path (because tempfile.mkdtemp uses different paths on different systems)
- The gpg binary is not guaranteed to be on /usr/bin/gpg and the PATH is trimmed on the tests init, so we have to detect gpg for the tests to run

The tests run fine now on Mac and Linux here
Yea, I agree with you, but we could also:
- fallback to the old argument '/usr/bin/gpg'
- raise an Exception (because all the tests will fail without the gpg binary)

what do you think?