Use canonical name for coverage job
Use canonical name for coverage job

Use "cover" for the coverage tox environment.  Also removed the unused
tox environment previously using "cover" as the name.

Change-Id: I48be7f673ad701c3b506548c1c30e51a076054b0

jmvrbanac/barbican,MCDong/barbican,jmvrbanac/barbican,cneill/barbican,cloudkeep/barbican,openstack/barbican,cloudkeep/barbican,MCDong/barbican,cneill/barbican,openstack/barbican