LU-6589 llapi: ..._layout_pattern_set() rejects valid patterns

LU-6589 llapi: ..._layout_pattern_set() rejects valid patterns

A typo in the input validation code causes llapi_layout_pattern_set()
to reject valid pattern values. Correct the typo and add related test
coverage in llapi_layout_test.c.

Signed-off-by: Ned Bass <bass6@llnl.gov>
Change-Id: I676a98b63d61fca114eacd882a19abce6f2cc857
Reviewed-on: http://review.whamcloud.com/14784
Reviewed-by: frank zago <fzago@cray.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>