LU-2904 tests: mount Lustre client with "32bitapi"

Mount Lustre client with "32bitapi" option while exporting a
filesystem with a 64-bit root inode. This is a temporary workaround
for LU-2904, and it should be removed when there is a patch that
fixes the NFS FSID generation problem.

Test-Parameters: envdefinitions=SLOW=yes,ENABLE_QUOTA=yes \
clientdistro=el6 serverdistro=el6 clientarch=x86_64 \
serverarch=x86_64 serverjob=lustre-b2_4 serverbuildno=12 \
testlist=parallel-scale-nfsv3,parallel-scale-nfsv4

Signed-off-by: Jian Yu <jian.yu@intel.com>
Change-Id: Ia26f3e3d23d901725ab175a6d370f58a1a93519c
Reviewed-on: http://review.whamcloud.com/6457
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>