viced: Move host quota calculation

Calculate this during initialization, not every time we want to use
it.

Change-Id: I931d2f3f0b4b99add682c098dd51f03c9942f5b4
Reviewed-on: http://gerrit.openafs.org/9710
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>