Fix macOS codesigning from Jenkins jobs

As seen in NXBT-3072, my comment explain the situation.

To summary, codesigning is working from SSH and VNC (IMO this is the proof that the setup is good), but not from a Jenkins job (using same user jenkins and same keychain file).

This is blocker for Nuxeo Drive release process.

For you tests, you can simply use:

• that job: https://qa.nuxeo.org/jenkins/job/Drive/job/Drive-packages/
• on that on that branch: wip-NXDRIVE-1873-remove-twang-from-ci

As Alexis proposed, a possible way to resolve this would be to use Jenkins addons such as https://wiki.jenkins.io/display/JENKINS/Keychains+and+Provisioning+Profiles+Plugin.