LU-3738 tests: improve posix.sh to support BASELINE_FS=zfs

LU-3738 tests: improve posix.sh to support BASELINE_FS=zfs

This patch improves posix.sh to support BASELINE_FS=zfs. It also
adds create_zpool(), create_zfs() and destroy_zpool() common
functions into test-framework.sh.

Test-Parameters: envdefinitions=SLOW=yes \
mdtfilesystemtype=zfs mdsfilesystemtype=zfs ostfilesystemtype=zfs \
ostcount=2 testlist=posix

Signed-off-by: Jian Yu <jian.yu@intel.com>
Change-Id: Ib8b3cf988bd7066a84a6f9f50ccc159ffeab6e0e
Reviewed-on: http://review.whamcloud.com/8323
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>