Skip backoff when exhausting ID uniqueid

Uniqueid exhaustion within a partition has nothing to do with backend
workload.  At most, we should wait the default backoff before
retrying; an increasing backoff is definitely not warranted.  This
commit removes any sort of backoff after an ID allocation attempt in
which all storage backend requests succeed but the uniqueid turns out
to be exhausted.
Revert IDAllocation wait time to 10 ms

Effectively reverts 143b20dc4e0aff75a2599bc4ead06c546f81022c

Commits incoming that allow module-specific overrides of timeout
values
Experimental util to override config opts in tests

I often want to set higher lock wait and id allocation wait times when
running tests on EC2 m1.mediums running CI, since Cassandra writes
that take 175 ms seem common (1/2 of test runs?  eyeballing a list of
recent runs, not being rigorous here), but that's an excessive wait
time on my workstation.  I'm adding an experimental test utility class
that reads a config file path (possibly relative path) from an
environment variable and reads a config from the file.  Test classes
where overridden config settings could be useful (anything that's
timeout sensitive) can pass a WriteConfiguration to the utility class
to have the overrides applied.

Initially tried to used MergedConfiguration but went insane trying to
navigate the configuration type hierarchy.  Gave up after an hour and
went with modifying a single WriteConfiguration.