ceph: integration: kill process grp on file-test

The file-test pod still hangs sometimes when exiting. Instead of
trapping SIGTERM as before, use tini's `-g` option to kill the process
group. According to further reading on bash signal handling [1], Ctrl-C
sends a kill signal to the entire process group in order to kill `sleep`
commands.

[1] Link also noted in code comments:
http://mywiki.wooledge.org/SignalTrap#When_is_the_signal_handled.3F

Signed-off-by: Blaine Gardner <blaine.gardner@suse.com>

tests/integration/ceph_base_file_test.go

@@ -178,16 +178,10 @@ spec:
     image: krallin/ubuntu-tini
     command:
         - "/usr/local/bin/tini"
+        - "-g"
         - "--"
-        - "bash"
-        - "-c"
-        - |
-          pid=
-          trap 'exit 0' SIGTERM
-          trap '[[ $pid ]] && kill "$pid"' EXIT
-          sleep 1800 & pid=$!
-          wait $pid
-          pid=
+        - "sleep"
+        - "1800"
     imagePullPolicy: IfNotPresent
     env:
     volumeMounts: