Adding timeout parameter to IDAuthority#getIDBlock

Instead of relying on a hardcoded retry count, getIDBlock now takes a
timeout long and accompanying TimeUnit.  Implementations return if
they are unable to allocate a block within the timeout duration.  But
really only the ConsistentKeyIDManager implementation respects the
timeout; MockIDManager doesn't bother.

I think idApplicationRetryCount could be refactored with a more
descriptive name now, since its only function is to limit the number
of randomized unique id exhaustions allowed before declaring the whole
partition exhausted.
Deleting old commented method from IDAuthority
Renaming idauthority-retries to match new purpose

The consistent key ID manager will now retry an allocation as many
times as possible before its timeout argument elapses;
idauthority-retries is now idauthority-uniqueid-retries and limits
only the number of randomized unique ids Titan tries within a
partition before assuming the whole partition is exhausted.
Setting exponential growth in getIDBlock backoff

Failures in getIDBlock now cause the method to wait for a backoff
period that doubles with every failure, starting at
idApplicationWaitMS and capped at 16 * idApplicationWaitMS.  This
gives six steps total (1, 2, 4, 8, 16, 32).