test : Fix for spurious failure

Problem : Once the features.uss is enabled it does not wait for
the process to be created. And if we try to check for
the pid of the snapd then it will not be present which
causes a failure.

Solution : Adding a EXPECT_WITHIN which waits to get the pid
until certain time period.

Change-Id: If075860173a996f9eee13b346e939686b94ec3f6
BUG: 1145450
Signed-off-by: Sachin Pandit <spandit@redhat.com>
Reviewed-on: http://review.gluster.org/8814
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>