More usage of ostestr and cleanup an unused dependency

Use ostestr as runner instead of the custome pretty_tox.sh script
(pretty much removed everywhere). pretty_tox3.sh is just a wrapper
for ostestr but it could be probably removed as well going forward.
Also remove the tempest-lib dependency, which originally provided
subunit-trace (now from os-testr).

Change-Id: I4390964ce83167d634b80f696e82a0e199582ce6

tox.ini

@@ -22,20 +22,20 @@ deps = -r{toxinidir}/test-requirements.txt
 commands =
   find . -type f -name "*.pyc" -delete
 passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY OS_DEBUG GENERATE_HASHES
-# there is also secret magic in pretty_tox.sh which lets you run in a fail only
+# there is also secret magic in subunit-trace which lets you run in a fail only
 # mode. To do this define the TRACE_FAILONLY environmental variable.
 
 [testenv:py27]
 commands =
     {[testenv]commands}
-    bash tools/pretty_tox.sh '{posargs}'
-    env TEST_OSPROFILER=1 bash tools/pretty_tox.sh 'nova.tests.unit.test_profiler'
+    ostestr '{posargs}'
+    env TEST_OSPROFILER=1 ostestr 'nova.tests.unit.test_profiler'
 
 [testenv:py35]
 commands =
     {[testenv]commands}
     bash tools/pretty_tox3.sh '{posargs}'
-    env TEST_OSPROFILER=1 bash tools/pretty_tox.sh 'nova.tests.unit.test_profiler'
+    env TEST_OSPROFILER=1 ostestr 'nova.tests.unit.test_profiler'
 
 [testenv:pep8]
 basepython = python2.7
@@ -54,7 +54,7 @@ setenv = VIRTUAL_ENV={envdir}
        LANGUAGE=en_US
 commands =
   find . -type f -name "*.pyc" -delete
-  bash tools/pretty_tox.sh '{posargs}'
+  ostestr '{posargs}'
 
 # TODO(gcb) Merge this into [testenv:functional] when functional tests are gating
 # with python 3.5
@@ -77,7 +77,7 @@ setenv = VIRTUAL_ENV={envdir}
        LANGUAGE=en_US
 commands =
   find . -type f -name "*.pyc" -delete
-  bash tools/pretty_tox.sh '{posargs}'
+  ostestr '{posargs}'
 
 [testenv:genconfig]
 commands = oslo-config-generator --config-file=etc/nova/nova-config-generator.conf