tox: Use common 'command' definition for unit tests

Less LoC. Winning.

Change-Id: Icc1531d18ea1e0692c41320a98100bba92d7b48a
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>

tox.ini

@@ -31,22 +31,15 @@ passenv =
   OS_DEBUG GENERATE_HASHES
 # 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.
+commands =
+  stestr run {posargs}
+  env TEST_OSPROFILER=1 stestr run --combine --no-discover 'nova.tests.unit.test_profiler'
 
 [testenv:py27]
 commands =
-  stestr run {posargs}
-  env TEST_OSPROFILER=1 stestr run --combine --no-discover 'nova.tests.unit.test_profiler'
+  {[testenv]commands}
   stestr slowest
 
-[testenv:py36]
-commands =
-  stestr run {posargs}
-  env TEST_OSPROFILER=1 stestr run --combine --no-discover 'nova.tests.unit.test_profiler'
-
-[testenv:py37]
-commands =
-  {[testenv:py36]commands}
-
 [testenv:pep8]
 description =
   Run style checks.
@@ -285,5 +278,3 @@ deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt
   -r{toxinidir}/requirements.txt
-commands =
-  stestr run {posargs}