Charm messaging can be improved

[Peter Matulis]

When the ceph-proxy application is newly deployed the information printed under the Message column in `juju status` is:

Ensure FSID and admin-key are set

a) It does not mention the 'monitor-hosts' option.

b) When a value for the 'admin-key' option is provided the messaging does not change.

c) When a value for the 'fsid' option is provided the messaging changes to:

Ready to proxy settings

even though a value for the 'monitor-hosts' option has still not been provided.

Is it possible to have:

1. the messaging change according to what is currently missing?

2. the pieces of data to be referred to by their configuration options?:

Missing values for: 'admin-key', 'fsid', 'monitor-hosts'
Missing values for: 'admin-key', 'fsid'
Missing values for: 'admin-key'