Don't quote {posargs} in tox.ini
Don't quote {posargs} in tox.ini

Quotes around {posargs} cause the entire string to be combined into one
arg that gets passed to stestr. This prevents passing multiple args
(e.g. '--concurrency=16 some-regex')

Change-Id: I64a99925b076268be0a472a5dacd1fdb24b26023

openstack/oslo.cache,openstack/oslo.cache