LU-3308 tests: fix sanity/sanityn test_mkdir() usage

LU-3308 tests: fix sanity/sanityn test_mkdir() usage

Remove "-p" option from test_mkdir() calls that do not need it.
test_mkdir() has its own error checking, so no need for duplicate
error checking in the caller as well.

Clean up script style for tests related to test_mkdir() changes:
- use $(...) instead of `...` for subshells
- use $tdir and $tfile for test filenames
- add useful messages to error() calls
- replace use of $SETSTRIPE wrapper with $LFS setstripe
- remove trailing "===" from test names
- use tabs for indentation instead of spaces

Combine sanity test_99[a-f] into test_99 to avoid duplicate checks.

Test-Parameters: trivial testlist=sanityn
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Steve Guminski <stephenx.guminski@intel.com>
Change-Id: I38d47f0c2e18aa20a0468f354ed88b740b3e17b8
Reviewed-on: https://review.whamcloud.com/26212
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>