Don't report async pendings on exception

If we encounter an exception trying to gather async pendings 'async'
doesn't exist and the cronjob ends up erroring out and leaving behind a
stale lock file.

Change-Id: I70a6d3f00bd2c9ce742e6d16af93804280707040
Whitelist external netifaces requirement

* tox.ini(testenv.install_command): Use the --allow-external and
--allow-insecure options so that pip 1.5 and later will assent to
retrieve the netifaces package even though it's not hosted on PyPI.
The --allow-insecure option is aliased to a clearer
--allow-unverified wording in 1.5, but the old form is being used to
avoid breaking users of 1.4.x and will be valid at least through
1.6.x according to comments in the pip source.

Change-Id: I587b516f3f77c930475ca2eaae5ff73c5d2ab576
Merge "Don't report async pendings on exception"