LU-7813 utils: improve lfs setstripe pool error message

LU-7813 utils: improve lfs setstripe pool error message

When a specified OST is not in the requested pool, improve the error
message printed to the user.  Currently it only prints:

  $ lfs setstripe -p audio -i 1 /myth/foo
  error: setstripe: create file '/myth/foo' failed

but this doesn't indicate why it failed.  Add in more information:

  error: setstripe: create file '/myth/foo' failed: OST not in pool?
  error: setstripe: create file '/myth/foo' failed: permission denied

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I409739b1e3dad633f0b0a4c4f94a746c0b6485bd
Reviewed-on: http://review.whamcloud.com/18965
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Frank Zago <fzago@cray.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>