[CLI] Update `pazuzu compose` CLI interface

[netme]

Currently pazuzu compose step is split into 2 parts: compose (creates Pazuzufile) and build (creates Dockerfile based on Pazuzufile). That gives to the end user some additional work.

Move build step inside compose step to follow the CLI interface:

$ pazuzu compose

NAME:
   pazuzu compose - Compose Dockerfile which Includes Given Features

USAGE:
   pazuzu compose [-d destination] [build flags]

   Build flags
   	-a  feature1,feature2,...
   	    adds new featurs to existing Pazuzufile
   	-i  feature1,feature2,...
   		inits/re-creates Pazuzufile with given set of features

DESCRIPTION:
   Compose step takes list of features as input, validates feature dependencies and creates both Pazuzufile and Dockerfile.

[olafmaurer]

Isn't this completed? I suggest closing.

[netme]

Yeah, makes sense