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: Ieeae90ecbd4f89cbff0513dcd949a0c1a8e8d8c1
(cherry picked from commit 3b954791e4)

tox.ini

@@ -20,7 +20,7 @@ deps =
        -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 commands = find . -type f -name "*.pyc" -delete
-           stestr run '{posargs}'
+           stestr run {posargs}
            stestr slowest
 whitelist_externals = find
 
@@ -70,7 +70,7 @@ commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasen
 
 [testenv:functional]
 basepython = python3
-commands = stestr run '{posargs}'
+commands = stestr run {posargs}
 setenv =
   {[testenv]setenv}
   OS_TEST_PATH = ./cinderclient/tests/functional