mon: make create a subcommand

We don't have other subcommands, but this establishes constency with
'osd create ...' and so on.

Signed-off-by: Sage Weil <sage@inktank.com>
cli: verbose by default, -q to shut up

Closes: #3907
Signed-off-by: Sage Weil <sage@inktank.com>
cli: part -n, --dry-run

Signed-off-by: Sage Weil <sage@inktank.com>
new: catch hostname lookup exception

Signed-off-by: Sage Weil <sage@inktank.com>
discover: implement -n

Not so useful, but...

Signed-off-by: Sage Weil <sage@inktank.com>
new: add -n

Say what files will be written, but don't.

Signed-off-by: Sage Weil <sage@inktank.com>
zapdisk: quick comment

Signed-off-by: Sage Weil <sage@inktank.com>
osd: fix no journal case

Behave is journal=None.

Signed-off-by: Sage Weil <sage@inktank.com>
install: generalize for any Debian and Ubuntu

All we need to do is decide to use APT and pass the codename down.

Part of #3920.

Signed-off-by: Sage Weil <sage@inktank.com>