main/openssh: fix openrc error on shutdown

The pgrep used to find and close ssh connections on shutdown also returns the pid of an openrc process. Sending SIGTERM to that pid causes an error message on shutdown: sshd: caught SIGTERM, aborting

Adding the colon to the command name prevents the openrc pid from being mistaken as an active ssh connection (it includes /etc/init.d/sshd in the command name).

I've tested this change both with and without active ssh connections. Active ssh sessions are still terminated as intended and you no longer get a "Shutting down ssh connections" message when there are none.

Closes #9261 (closed)