CLI usability: Parse compound operation parameters

Currently, CLI does not parse compound operation parameters and relies on ModelNode.fromString() method.

This means that an user have to use "key" => "value" notation to denote compound parameters. This is inconsistent with the rest of CLI using key="value" notation.

As an example, to add https connector one needs to use:

/subsystem=web/connector=https:add(socket-binding=https, scheme=https, protocol="HTTP/1.1", enabled=true, ssl=

{ "certificate-key-file" =>"/tmp/test.key"}

))

command instead of more straightforward:

/subsystem=web/connector=https:add(socket-binding=https, scheme=https, protocol="HTTP/1.1", enabled=true, ssl=

{certificate-key-file="/tmp/test.key"}

))

This is never documented.

Also any exceptions thrown by ModelNode.fromString() are discarded. I think they should be reported back to the user. (DefaultCallbackHandler lines 448-453)