scheduler: Reset HostID when placing jobs
scheduler: Reset HostID when placing jobs

This is particularly problematic if we fail to place an omni job,
because subsequent placements will treat all hosts as having the
requested number of omni jobs, and a host will be picked at random,
leading to stopSurplusOmniJobs stopping the job just placed and leading
to flapping jobs.

Signed-off-by: Lewis Marshall <748e1641a368164906d4a0c0e3965345453dcc93@lmars.net>

flynn/flynn,philiplb/flynn,philiplb/flynn,lmars/flynn,lmars/flynn,philiplb/flynn,flynn/flynn,flynn/flynn,flynn/flynn,philiplb/flynn,flynn/flynn,lmars/flynn,lmars/flynn,lmars/flynn,philiplb/flynn