LU-8649 recovery: print some useful messages in recovery

LU-8649 recovery: print some useful messages in recovery

To make it more clear to the admins that recovery won't start
until the first client connects, this patch prints the following
useful messages in recovery, in case the admins are waiting for
recovery to complete:
- a console message every 10 minutes or so, and
- adding status WAITING_FOR_CLIENTS to /proc recovery_status file

Change-Id: I03d37b4c00a799a1fd651b8d60cdbceed807cea1
Signed-off-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-on: https://review.whamcloud.com/30656
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>