Revert "tox: Don't create '.pyc' files"

This reverts commit 0d6d1616b9.

The PYTHONDONTWRITEBYTECODE setting is ignored in post-v1.6.0 versions
of tox due to issues with setuptools [1]. Suffer the performance hit.

[1] https://tox.readthedocs.io/en/latest/changelog.html#id21

Change-Id: I99d165f0cc4f5382aef72f21f31bc985585f4748

tox.ini

@@ -7,18 +7,19 @@ skipsdist = True
 usedevelop = True
 # tox is silly... these need to be separated by a newline....
 whitelist_externals = bash
+                      find
                       rm
 install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
 setenv = VIRTUAL_ENV={envdir}
          OS_TEST_PATH=./nova/tests/unit
          LANGUAGE=en_US
          LC_ALL=en_US.utf-8
-         PYTHONDONTWRITEBYTECODE=1
 deps = -r{toxinidir}/test-requirements.txt
 # NOTE(mriedem): If py34 fails with "db type could not be determined", delete
 # .testrepository and try again. Running py34 before py27 is OK, but not the
 # other way around. See: https://bugs.launchpad.net/testrepository/+bug/1212909
 commands =
+  find . -type f -name "*.pyc" -delete
   py27: bash tools/pretty_tox.sh '{posargs}'
   py{34,35}: bash tools/pretty_tox3.sh '{posargs}'
 passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY OS_DEBUG GENERATE_HASHES
@@ -39,6 +40,7 @@ setenv = VIRTUAL_ENV={envdir}
        OS_TEST_PATH=./nova/tests/functional
        LANGUAGE=en_US
 commands =
+  find . -type f -name "*.pyc" -delete
   bash tools/pretty_tox.sh '{posargs}'
 
 [testenv:api-samples]
@@ -49,6 +51,7 @@ setenv = VIRTUAL_ENV={envdir}
        OS_TEST_PATH=./nova/tests/functional/api_sample_tests
        LANGUAGE=en_US
 commands =
+  find . -type f -name "*.pyc" -delete
   bash tools/pretty_tox.sh '{posargs}'
 
 [testenv:genconfig]