Import the oslo looping call implementation (which is a copy of
nova's), delete nova's local copy, convert all users to the new
location.
It should be noted that the oslo implementation of
FixedIntervalLoopingCall measures time from the start of the
periodic task, not the end, so periodic tasks will run with a
constant frequency instead of the frequency changing depending on
how long the periodic task takes to run.
Change-Id: Ia62ce1988f5373c09146efa6b3b1d1dc094d50c4
c4596b37e8