Harmonize PEP8 checking between tox and run_tests.sh

Tox and run_tests.sh were running PEP8 checks against different
file-sets. This patch refactors the logic to determine which files to
run PEP8 checks on into `tools/run_pep8.sh` where it can be called by
both tox and `run_tests.sh`.

Additional fixes:

Some of our Python XenAPI Dom0 plugins don't end in *.py but should
still be checked by PEP8. This patches fixes the hacking.py violations
in the files and adds them back to the srcfiles list.

Merged tools/unused_imports.sh into tools/run_pep8.sh

Change-Id: Id5edd1acb644ab938beffc3473494a179d9d8cda

tox.ini

@@ -18,18 +18,7 @@ downloadcache = ~/cache/pip
 deps=
   pep8==1.3.3
   pyflakes
-commands =
-  python tools/hacking.py --doctest
-  python tools/hacking.py --ignore=E12,E711,E721,E712,N403,N404,N303 \
-    --show-source \
-    --exclude=.venv,.git,.tox,dist,doc,*openstack/common*,*lib/python*,*egg,build,./plugins/xenserver/networking/etc/xensource/scripts,./plugins/xenserver/xenapi/etc/xapi.d/plugins .
-  python tools/hacking.py --ignore=E12,E711,E721,E712,N403,N404,N303,N304 \
-    --show-source \
-    ./plugins/xenserver/networking/etc/xensource/scripts \
-    ./plugins/xenserver/xenapi/etc/xapi.d/plugins
-  python tools/hacking.py --ignore=E12,E711,E721,E712,N403,N404,N303 \
-    --show-source --filename=nova* bin
-  bash tools/unused_imports.sh
+commands = bash tools/run_pep8.sh
 
 [testenv:pylint]
 setenv = VIRTUAL_ENV={envdir}