LU-1227 tests: mds-survey.sh should check ost's space

LU-1227 tests: mds-survey.sh should check ost's space

When we run the test with stripe_count=1, we need to
reduce the file_count to be the min of both mdt's inode
and ost's inode

Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Change-Id: I04a558c277ebf9a1e1526a7d507faab8b66e740c
Reviewed-on: http://review.whamcloud.com/2372
Tested-by: Hudson
Reviewed-by: Yu Jian <yujian@whamcloud.com>
Reviewed-by: wangdi <di.wang@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>