LU-9221 jobstats: Create a pid-based hash for jobid values

LU-9221 jobstats: Create a pid-based hash for jobid values

Use cfs_hash_table to create a pid to jobID based mapping.
Change default behavior of JobIDs to default to procname_uid if
a suitable value cannot be found in the environment.

All entries older than RESCAN_INTERVAL  seonds are refreshed
on access.
Items can be purged by writing to procfs_name.
"" will remove all entries
When purging the cache, items older than DELETE_INTERVAL are
deleted.

Signed-off-by: Ben Evans <bevans@cray.com>
Change-Id: I22e9d73c4585d7c5496829bc20bce191304e0d58
Reviewed-on: https://review.whamcloud.com/25208
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andrew Perepechko <andrew.perepechko@seagate.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>