Tweak test timing

In test15.17, an salloc spawns an sbatch within that same job
allocation then exits. This results in a race condition which
can cause the terminate job RPC from slurmctld to slurmd to
briefly hang and mark the node non-responsive, causing later
tests that may need the node to fail (timeout waiting for
job allocation). A sleep is added to the salloc here to give
the batch job a chance to begin and clean up the job allocation
quickly.

testsuite/expect/test15.17

@@ -74,6 +74,11 @@ expect {
 		exp_continue
 	}
 	-re "Submitted batch job ($number)" {
+#
+#		Sleep gives time for the batch job to start and prevents a race
+#		condition that can briefly leave node in a not responding state
+#
+		sleep 1
 		set job_id_2 $expect_out(1,string)
 		send "exit \r"
 		exp_continue