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.

This reverts commit e7b48c0b.

This reverts commit 201d238a.

See merge request !1212