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: I7e59181ef5f3926c6a8799ac4f6c775d04350a99
Reviewed-on: http://review.whamcloud.com/8180
Tested-by: Jenkins
Reviewed-by: Minh Diep <minh.diep@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>