LU-1134 test: can not assume lustre setup before nfs test

LU-1134 test: can not assume lustre setup before nfs test

During autotest, lustre can be unmounted. parallel-scale-nfs
test should not assume that lustre is mounted and skip the setup.

Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Change-Id: I79bd995efd9f08b27ec8c08ac7087be78d578a36
Reviewed-on: http://review.whamcloud.com/2218
Tested-by: Hudson
Reviewed-by: Wei Liu <sarah@whamcloud.com>
Reviewed-by: Yu Jian <yujian@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>