Set pipefail for wrapper scripts

Previously if the testr list command was failing subunit2py would
return a 0 making the test runs that use the pretty_tox scripts also
return 0 despite testr actually failing. This commit gets around this
condition by setting pipefail in the pretty_tox scripts to ensure that
we actually fail.

Change-Id: I9cbaf83cfea7c02133b27fe639e7ea12edb48f7e
diff --git a/tox.ini b/tox.ini
index 9389cf4..1d7e1b7 100644
--- a/tox.ini
+++ b/tox.ini
@@ -31,19 +31,19 @@
 # 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.sh '(?!.*\[.*\bslow\b.*\])(^tempest\.(api|scenario|thirdparty|cli)) {posargs}'
+  bash tools/pretty_tox.sh '(?!.*\[.*\bslow\b.*\])(^tempest\.(api|scenario|thirdparty|cli)) {posargs}'
 
 [testenv:testr-full]
 sitepackages = True
 commands =
-  sh tools/pretty_tox.sh '(?!.*\[.*\bslow\b.*\])(^tempest\.(api|scenario|thirdparty|cli)) {posargs}'
+  bash tools/pretty_tox.sh '(?!.*\[.*\bslow\b.*\])(^tempest\.(api|scenario|thirdparty|cli)) {posargs}'
 
 [testenv:heat-slow]
 sitepackages = True
 setenv = OS_TEST_TIMEOUT=1200
 # The regex below is used to select heat api/scenario tests tagged as slow.
 commands =
-  sh tools/pretty_tox_serial.sh '(?=.*\[.*\bslow\b.*\])(^tempest\.(api|scenario)\.orchestration) {posargs}'
+  bash tools/pretty_tox_serial.sh '(?=.*\[.*\bslow\b.*\])(^tempest\.(api|scenario)\.orchestration) {posargs}'
 
 [testenv:large-ops]
 sitepackages = True
@@ -79,7 +79,7 @@
 [testenv:smoke]
 sitepackages = True
 commands =
-   sh tools/pretty_tox.sh '(?!.*\[.*\bslow\b.*\])((smoke)|(^tempest\.scenario)) {posargs}'
+   bash tools/pretty_tox.sh '(?!.*\[.*\bslow\b.*\])((smoke)|(^tempest\.scenario)) {posargs}'
 
 [testenv:smoke-serial]
 sitepackages = True
@@ -87,7 +87,7 @@
 # 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 '(?!.*\[.*\bslow\b.*\])((smoke)|(^tempest\.scenario)) {posargs}'
+   bash tools/pretty_tox_serial.sh '(?!.*\[.*\bslow\b.*\])((smoke)|(^tempest\.scenario)) {posargs}'
 
 [testenv:stress]
 sitepackages = True