shill: wimax: Don't ask users to re-enter credentials if available.

shill now sets the PassphraseRequired to true only if credentials are
not available, or if a connect attempt to a live network failed. Also,
refuse connecting to a service that's marked as non-connectable, and
fix UpdateConnectable in WiMaxService::Start.

BUG=chrome-os-partner:10115
TEST=unit tests

Change-Id: I53989736a82e4062422c648c58ccc83abc045a86
Reviewed-on: https://gerrit.chromium.org/gerrit/24187
Reviewed-by: Darin Petkov <petkov@chromium.org>
Tested-by: Darin Petkov <petkov@chromium.org>
diff --git a/mock_wimax_service.h b/mock_wimax_service.h
index 52d1453..5f3860b 100644
--- a/mock_wimax_service.h
+++ b/mock_wimax_service.h
@@ -24,6 +24,7 @@
   MOCK_METHOD0(Stop, void());
   MOCK_CONST_METHOD0(IsStarted, bool());
   MOCK_METHOD1(SetState, void(ConnectState state));
+  MOCK_METHOD0(ClearPassphrase, void());
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MockWiMaxService);