EX-3838 test: sanity-pumount races

EX-3838 test: sanity-pumount races

In sanity-pumount, add functions wait_for_open(), wait_for_exec(), and
wait_for_mmap() to wait for the forked PID to exec, open, or mmap the
file on the Lustre FS. Use these to prevent fork exec check races.

Test-Parameters: trivial testlist=sanity-pumount,sanity-pumount,sanity-pumount,sanity-pumount clientextra_install_params="--packages pumount"
Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: I2a89989521cc4e61d35799c1d4fdb8ce37ae12d9
Reviewed-on: https://review.whamcloud.com/47344
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>