LU-2153 quota: several fixes for reintegration

LU-2153 quota: several fixes for reintegration

- On master side, never delete the id entry from the global/slave
  index, otherwise, those deleted entries will not be transfered
  during reintegration, and improved test_7a for this change;
- When start reintegration thread, if there is any pending
  updates, abort and try to start reintegration later;
- Set rq_no_retry_einprogress for quota request;
- When master found quota acquire for not enforced ID, return
  -ESRCH to slave instead of -EINPROGRESS;
- Check free inodes in test_2;

Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: I64037f6aff6be686250272eda53c027bf5ba47c2
Reviewed-on: http://review.whamcloud.com/4275
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>