Support systemd status to return 0 exit code when status OK #4

[seglo]

CentOS 7 uses systemd. For some reason even when the cassandra service is running OK, a service cassandra status will return a non-zero exit code which causes the Ambari status handler to fail. This fix will use systemctl to get the status when it exists on the path.

[ajak6]

Let me test this out on some test Cluster. But if we will use systemctl, then I will use the same to start and stop the service as well. Although I tried using the current code on my centos 7 image and it is working without issues.

[NPraneeth]

It does not work on my centos 7.2 . But with this change it is working fine. I also think the start and stop should also accommodate this change.