Dispatcher service check should escape DB_NAME with backticks

[gl]

In case the DB_NAME includes a special char, like "-", it is necessary to escape the database name with backticks. The following line should therefore be backslashbacktick${DB_NAME}backslashbacktick (sorry, github formatting is messing with the chars :)) Otherwise, the check fails and dispatcher service shuts down.

https://github.com/librenms/docker/blob/0540fd9512885f4f48c5a4c6c7212ed17f6a9223/rootfs/etc/cont-init.d/05-svc-dispatcher.sh#L73

[crazy-max]

SGTM, contribs welcomed