Make tox jobs runnable concurrently

Will speed up run of tox jobs when several jobs are proposed
simultaneously.

Updates:

analytics-geowiki-tox-flake8
analytics-limn-mobile-data-tox-flake8
analytics-multimedia-tox-flake8
analytics-quarry-web-tox-flake8
analytics-wikimetrics-tox-flake8
analytics-wp-zero-tox-flake8
apps-android-wikipedia-tox-flake8
integration-zuul-config-tox-py27
labs-tools-extdist-tox-flake8
labs-tools-gblrenamemon-tox-flake8
mwext-EventLogging-tox-flake8
mwext-EventLogging-tox-py27
mw-tools-release-tox-flake8
mw-tools-release-tox-py27
mw-tools-releng-tox-doc
mw-tools-scap-tox-doc
mw-tools-scap-tox-flake8
mw-tools-scap-tox-py27
operations-puppet-tox-data_admin_lint
pywikibot-bots-CommonsDelinker-tox-flake8
pywikibot-core-tox-flake8
pywikibot-core-tox-flake8-docstrings
pywikibot-core-tox-nose
wikimedia-bots-jouncebot-tox-flake8

Change-Id: I25178c892d57263ca819a93ad9f3f72984259e6f