Instead of sorting hosts by score, find max score and choose one of
the hosts with max score directly. Saves a little time on sorting and
avoids extra copying of HostPriorityList entries.
Test had to be updated as one of the test cases relied on having a
stable order from pre-sorting.
To improve the throughput of current scheduler, we can do
a simple optimization by calcluating priorities in parallel.
This doubles the throughput of density test, which has the default
config with 3 priority funcs (the spreading one does not actually
consume any computation time). It matches the expectation.
The "Combined requested resources" message becomes excessive as
the cluster fills up, drop it down to V(2)
Put an explicit V(2) on the only other scheduler Infof call that didn't
have V specified already.
A lot of packages use StringSet, but they don't use anything else from
the util package. Moving StringSet into another package will shrink
their dependency trees significantly.
Having no nodes in the cluster is unusual and is likely a test
environment, and when a pod is deleted there is no need to log
information about our inability to schedule it.
