Support starting and stopping corosync-notifyd

[inouekazu]

This patch allows corosync-notifyd to be started with pcs cluster start. Addressed issues pointed out at https://github.com/ClusterLabs/pcs/pull/296#issuecomment-858555922.

[knet-ci-bot]

Can one of the admins verify this patch?

[tomjelinek]

Thank you for the patch. We are quite busy right now, but we will get back to you and take a closer look at the patch hopefully in a few weeks.