add uwsgi provider for WSGI applications
use a single validation error handling function
add one role validation method to be used in child objects
use a validation_error method which also does logging
extend drop target to include the box of servers

Fixes bnc#838662
added methods for validating the existence of a db proposal
allow comma-separated lists as well as space separated ones
extending 'wait for chef' for other states
during node edit, offer user to define intended node role
timeout must be integer
remove comment from xml config
added network role
network role
show Undecided label for no_role
this feature allow on build stage download and cache python packages required by crowbar.yml (pips directive) of all barclamps