tests: Check if vlserver died during startup

tests: Check if vlserver died during startup

Currently, the volser/vos test starts a local vlserver to communicate
with. If the vlserver dies during startup, the spawned 'vos'
subprocesses take forever to run, since we need to wait for our Rx
calls to timeout for every operation.

To make it less annoying to detect and investigate errors that might
cause the vlserver to fail during startup, check if the vlserver dies
right away. We already sleep for 5 seconds when starting the vlserver,
so just check if the pid still exists after those 5 seconds.

Change-Id: I6c33059542fa975e4cb389b718f9da190cd13289
Reviewed-on: https://gerrit.openafs.org/13942
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>