test: fix flaky crashing.sh

Two races, both around the post:script Finit runs when it gives up on a
service.

Finit marks the service crashed before it forks post:script, so the file
the test greps for lands a moment later.  Waiting for the state is not
enough.

slay then takes the PID from initctl status, and service_post_script()
sets svc->pid to the script's PID, so once Finit has given up the PID
reported for the service is the post:script.  Killing that takes out the
script instead of the service and the file never arrives at all.  The
guard for this was already there, with a comment describing it, but
inside the loop that waits for a PID to appear, so it only covered the
case where there was none.  A PID that was already there went straight
to kill -9.  Hence the gcc leg killing once more at lap 13, after Finit
had stopped restarting, where clang stopped at 12.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

test/crashing.sh

@@ -8,7 +8,7 @@ TEST_DIR=$(dirname "$0")
 test_teardown()
 {
     say "Running test teardown."
-    run "rm -f $FINIT_CONF" "/tmp/post"
+    run "rm -f $FINIT_CONF /tmp/post"
 }
 
 crashit()
@@ -48,8 +48,7 @@ test_one()
     fi
 
     retry "assert_status $nm crashed" 500
-    run "cat /tmp/post"
-    assert_file_contains "/tmp/post" "POST"
+    retry "assert_file_contains /tmp/post POST" 100
     run "rm -f /tmp/post"
 }