Simplify cinder manage command args

The 'cinder manage' command argumenst are kind of a disaster.
The positionals are <host> <id> where <id> is undefined/free form
K/V pairs.  On top of it we then have --source-name and --source-id
optional arguments available.  There absolutely no way to tell from
the help what one should be entering here without referring to the
code, and even then it's not quite clear how the options work and
which one will be used.

To clean this up, change the positionals to <host> <identifier>
where both are strings.  Remove --source-name and --source-id
and consolidate those options with --id-type.

id-type will allow a user to specify the type of identifier
(source-name, source-id, or whatever), but defaults to
source-name which is most commonly used currently.

* NOTE *
Ideally we'd just do away with the designator source-name/source-id
altogether and just have an <identifier> positional arg.  Each driver
would then be responsible for figuring out what was passed an how to
deal with it.  This however requires changes in all of the drivers and
broader changes on the Cinder side which I don't think are warranted
during RC.

During Kilo we should clean all of this up, but for now at least the
syntax is somewhat ready for human consumption and a bit easier than
what we introduced.

Change-Id: I07696648ae647f17ab9180cd87b25f8cb888f5d6
Closes-Bug: 1376311