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. This is needed so tempest can migrate to using
tempest-lib. The stable jobs run with tempest master, however since
tempest-lib isn't in requirements for the stable branches these jobs
can't pass which blocks the tempest changes from landing.

Change-Id: Iaf6228a5e0968e9578abd93d2d0e47cf6a089c75
(cherry picked from commit ed1126717eedfed036888aa56f4fc6000b4fc6a6)
Merge "Add tempest-lib as a global requirement and a tracked project" into stable/icehouse