Use ostestr instead of the custom pretty_tox.sh

Switch to os-testr as wrapper of testr, instead of the custom
script pretty_tox.sh.

Change-Id: Ia9b8860f4cbbc5500f35a0a59c2d2ef1089b8415

test-requirements.txt

@@ -14,6 +14,7 @@ fixtures>=1.3.1 # Apache-2.0/BSD
 mock>=1.2 # BSD
 oslosphinx!=3.4.0,>=2.5.0 # Apache-2.0
 oslotest>=1.10.0 # Apache-2.0
+os-testr>=0.4.1 # Apache-2.0
 psycopg2>=2.5 # LGPL/ZPL
 pylint==1.4.5 # GNU GPL v2
 reno>=0.1.1 # Apache2

tox.ini

@@ -12,8 +12,7 @@ setenv =
 deps =
     -r{toxinidir}/requirements.txt
     -r{toxinidir}/test-requirements.txt
-commands = bash tools/pretty_tox.sh '{posargs}'
-whitelist_externals = bash
+commands = ostestr {posargs}
 passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
 
 [testenv:cover]