LU-1484 lprocfs: enable HAVE_PROCFS_USERS for rhel kernels

LU-1484 lprocfs: enable HAVE_PROCFS_USERS for rhel kernels

For rhel kernels, given only the kernel-devel rpm it is not possible
to tell if proc_dir_entry_aux is defined, so assume it is.  It has
been included since late in the 5.x release cycle.

Test-Parameters: envdefinitions=SLOW=yes clientdistro=el5 \
  serverdistro=el5 clientarch=x86_64 serverarch=x86_64 \
  testlist=recovery-small

Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: If17ecb0902ec90a1af6228d2b9b1b72bc68a6672
Reviewed-on: http://review.whamcloud.com/5439
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>