During the upgrade from Queens there can be some wrong config
remainings. One of them is the existence of /etc/corosync/
corosync.conf as a directory. This will cause pacemaker to fail
when the node is upgrade to Train, failing with:
Error:Unable to read /etc/corosync/corosync.conf: Is a directory.
This patch checks during the upgrade if the file exists and it is
a directory. In that case, it will get removed.