Switch gating tox jobs to testr parallel

This commit will migrate all gating tox jobs to use testr with the
--parallel flag. The smoke tox job is left serial because neutron
doesn't work with tempest in parallel.

Part of bp speed-up-tempest

Change-Id: I1e6eb9c7ce4d55010844ce3b6ca10dd20e7359b4
diff --git a/tox.ini b/tox.ini
index 471fecb..185d507 100644
--- a/tox.ini
+++ b/tox.ini
@@ -19,7 +19,7 @@
 # The regex below is used to select which tests to run and exclude the slow tag:
 # See the testrepostiory bug: https://bugs.launchpad.net/testrepository/+bug/1208610
 commands =
-  sh tools/pretty_tox_serial.sh '(?!.*\[.*\bslow\b.*\])(^tempest\.(api|scenario|thirdparty|cli)) {posargs}'
+  sh tools/pretty_tox.sh '(?!.*\[.*\bslow\b.*\])(^tempest\.(api|scenario|thirdparty|cli)) {posargs}'
 
 [testenv:testr-full]
 sitepackages = True
@@ -53,6 +53,9 @@
 [testenv:smoke]
 sitepackages = True
 setenv = VIRTUAL_ENV={envdir}
+# This is still serial because neutron doesn't work with parallel. See:
+# https://bugs.launchpad.net/tempest/+bug/1216076 so the neutron smoke
+# job would fail if we moved it to parallel.
 commands =
    sh tools/pretty_tox_serial.sh 'smoke {posargs}'
 
@@ -61,7 +64,7 @@
 setenv = VIRTUAL_ENV={envdir}
 commands =
    python -m tools/tempest_coverage -c start --combine
-   sh tools/pretty_tox_serial.sh '(?!.*\[.*\bslow\b.*\])(^tempest\.(api|scenario|thirdparty|cli))'
+   sh tools/pretty_tox.sh '(?!.*\[.*\bslow\b.*\])(^tempest\.(api|scenario|thirdparty|cli))'
    python -m tools/tempest_coverage -c report --html {posargs}
 
 [testenv:stress]