delinting
requirements refresh and additional dateutil req for 957301
use PST instead of UTC when talking to bugzilla

Bugzilla runs on PST, so requesting time-sensitive data from it using
UTC means we occasionally miss changes that were made in PST evening.
This patch fixes that by getting the current PST/PDT time instead of
UTC before talking to BZ.
apply time zone formatting before interacting with bugzilla

apply the proper time zone formatting to the bugzilla cron and cron
tests for the happy path and degenerate case

fixes bug 957301
add comment about why we use PST
Merge pull request #1903 from lonnen/957301-bugzilla-cron

bug 957301 - refactor bugzilla cron
fixes bug 794548 - display "exploitability" rating in UI to logged-in users