Fix WifiInfoTest flakiness

Poll a bit longer waiting for getNetworkId and getWifiState to return
the proper values. The bug reports seem to indicate that the WiFi
is shutting down properly.

Add a new static check method to PollingCheck that I think is simpler
than the existing way of creating a new PollingCheck, overriding
check, and then making sure to call run. This new variation also allows
you to specify a message rather than just "unexpected timeout."

Bug 6443337

Change-Id: I9f7c942f6e26b957bb717b58b1ab984acc556bf7