If cluster name is not found, use default cluster name

We disable sql_log_bin while managing repman_slave_definition database and
destroying slave database. Else, changes are replicated which can break
slave node.

edgebot is dropped too, as it was shared instance implementation for edgetest.

Some Py2-SR like neoppod/stress-testing need Qemu but not Ceph.

Also note that the conditional [systemd-markupsafe-download] only works
if [systemd-python] uses the same Python as the one that runs buildout.

rbd functionality is enabled only on machines with supported libc version.

See merge request nexedi/slapos!1209

The mariadb/proxysql service automatically start when repman shut it down then
repman cannot check if service was correcty stopped because it's already up.
Stop a service will not work too.

It should be possible to add 2 or more cluster in the same instance

Rarely used https backend was missing the backend Via additions, thus it was
not transmitted there.