LU-7352 tests: conf-sanity 78 don't check missing files

Commit b666d02e13e stopped conf-sanity test_78 failing if all of
the required files could not be created.  However, the test also
checks later whether those files are still available after the
filesystem resize.  Reduce $num_files to match the number of
files actually created.

Test-Parameters: trivial envdefinitions=ONLY=78 testlist=conf-sanity,conf-sanity,conf-sanity,conf-sanity
Test-Parameters: trivial envdefinitions=ONLY=78 testlist=conf-sanity,conf-sanity,conf-sanity,conf-sanity
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I0ccfbd3f6597167c937e75cf9b5d0892cb5cab07
Reviewed-on: http://review.whamcloud.com/20558
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>