LU-2420 tests: Have POSIX testing on b1_8

LU-2420 tests: Have POSIX testing on b1_8

Have POSIX testing automated on b1_8 as it is on master.
LU-2274 port is included to change the baseline filesystem to ext3
for POSIX testing on SLES distro.
Also, this patch adds add_group() and add_user() functions into the
test-framework.sh. They are used by setup_posix_users() in posix.sh.

port of b2_1 patch f55a2af51af0bbb1d97e6987a45ca501adbc4ab6
port of b2_1 patch f9531ab0803cbafcb68003f3470307e4b826129f

Test-Parameters: envdefinitions=SLOW=yes testlist=posix

Signed-off-by: Liu Ying <emoly.liu@intel.com>
Change-Id: I8e3e8d5e87b13f4fd2d0b972d2161e9f1afbc4e9
Reviewed-on: http://review.whamcloud.com/4894
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Minh Diep <minh.diep@intel.com>
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>