Allow any unvalidated Network to satisfy NetworkRequests.

Explicitly selected Networks may never be validated (e.g. Chromecast)
but are still given a high score so they can explicitly become the
default Network.  Without this fix they do not become the default
Network if another Network is present.  This was an artifact of how
unvalidated Networks were handled, but now that unvalidated Networks
are properly handled, ala 50807d, we can freely rematch even
unvalidated Networks and NetworkRequests.
Also, never linger and teardown unvalidated Networks as the user
might be in the process of signing in.  This better matches prior
behavior when unvalidated networks didn't match NetworkRequests,
and thus were never lingered.
Also, don't disconnect networks that may be lingering.  The
disconnect logic in rematchNetworkAndReqeuests() is adjusted to only
fire when a network is newly validated.
It is incorrect to consider rematching uncreated Networks and
explicitly selecting created Networks, so this change logs error
messages in those cases.

bug:17647968
bug:17396616
Change-Id: Id6b8a350b8200f484d5bfd14ca0a8f64f08846a0