cephadm: edd exporter support to mgr/cephadm

cephadm: edd exporter support to mgr/cephadm

Several changes to introduce support for the exporter
1. new commands for generating/managing the config
settings required;
- generate-exporter-config (defaults)
- get-exporter-config
- clear-exporter-config
- set-exporter-config token/port
- set-exporter-tls (crt/key)

2. exporter is not a container, so a patch is added to the
run_cephadm method to 'tolerate' cephadm-exporter
daemons

3. the purge method is called on removal of a service. This has a default do-nothing response in CephService, but in
the CephadmExporter service, purge will remove it's config
from the mon store

4. during deploy (_create_daemon) a new remoto call to copy
the cephadm binary to the target is needed - prior to
invoking the deploy request

5. Default placement for the exporter is *, so by default once
the service is created, exporter daemons will appear on all
cluster nodes

Signed-off-by: Paul Cuzner <pcuzner@redhat.com>