tasks/cephfs: switch unmount timeout to 15 minutes

Our ffsb and fsync tests contain so many small writes at random offsets
that it can take >10 minutes to commit all of them to disk if we get
a slower OSD cluster. 15 minutes is still a plenty-fast timeout for
this stage compared to just hanging and losing the logs!

Signed-off-by: Greg Farnum <gfarnum@redhat.com>

tasks/cephfs/fuse_mount.py

@@ -236,7 +236,7 @@ def umount_wait(self, force=False):
         try:
             if self.fuse_daemon:
                 # Permit a timeout, so that we do not block forever
-                run.wait([self.fuse_daemon], 30)
+                run.wait([self.fuse_daemon], 900)
         except MaxWhileTries:
             log.error("process failed to terminate after unmount.  This probably"
                       "indicates a bug within ceph-fuse.")