Enable module specific command line parameters

Idea

Add a flags parameter to the create call and hand down textual or parsed JSON to the module. The JSON on the command line can either a) be associated with the module mention or it can b) be associated with the module kind's topic or c) have a separate flags section just for module flags.
Opinions?

Examples (prototyping, not claiming this grammar is ideal):

a)

slave --modules='[{lib : <path>, modules : [{name : "myModule", flags : '{credentials : "foo"}}]}]'

b)

slave --modules='[{lib : <path>, modules : [
{"myModule"}]}]' --authenticatorFlags='{credentials : "foo"}'

c)

slave --modules='[{lib : <path>, modules : [{"myModule"}
]}]' --moduleFlags='[{module : "myModule", flags :
{credentials : "foo"}
]}

In any case modules could report their required flags syntax when calling

slave --help --modules='[{lib : <path>, modules : [
{"myModule"} ]}]'

or something like that in any of the above variants.

This was copied from Bernd's comment on MESOS-1384.