Fix posargs usage for tox jobs

This commit removes the posargs from the coverage job's testr line
which will not work with the coverage periodic jenkins. It also adds
posargs to the 'all' job which will enable running a single test using
tox.

Change-Id: I650531377be7f58d18f79addefc32e62a4c268ea
Merge "Fix posargs usage for tox jobs"