Add tempest-lib as a global requirement and a tracked project

This commit adds tempest-lib to global requirements and also adds it
to project.txt. This will only be a test-requirement on projects,
except for tempest.

Change-Id: Iaf6228a5e0968e9578abd93d2d0e47cf6a089c75
Merge "Add tempest-lib as a global requirement and a tracked project"