Better handling of unvalidated networks.

Give unvalidated networks penalized scores and allow them to satisfy
requests.

Previously unvalidated networks were never allowed to satisfy
NetworkRequests and so never caused CONNECTIVITY_ACTION broadcasts.
Previously if there were no other networks present an unvalidated
network would still be made the default.  This change formalizes
this behavior using our existing network score logic by assigning
unvalidated networks a highly penalized score.

bug:16358003
bug:17364306
Change-Id: I28fcd6f5ac4b52a4d1c234c472cfa8ba998bcc6f