Backport - Juno - resolved issue with neutron ha failover cron clobbering other crons

the cron job for the neutron ha l3 failover is non blocking. this
makes it so that its possible to run many of the same job which
can cause all kinds of terribad issues. this agragates the jobs
into a single script that has a lock file such that it will only
ever run one of the single jobs.

Cherry picked from 851a38d1dc7e506b1967e03c6c4c667b9ece9bf7

Closes issue #383
Related issue #378