1. When a Wi-Fi network connected and receiving
intent android.settings.PROCESS_WIFI_EASY_CONNECT_QR_CODE,
show WifiDppAddDeviceFragment from WifiDppConfiguratorActivity
instead of WifiNetworkListFragment
2. Only handle intent when savedInstanceState is null
3. To show a fragment
I. do nothing when a fragment is already visible on screen,
II. pop back stack if it's in back stack, we can do this because
current fragment transactions are arranged in an order
Bug: 124194531
Test: atest WifiQrCodeTest
atest WifiDppConfiguratorActivityTest
atest WifiDppEnrolleeActivityTest
atest WifiDppQrCodeGeneratorFragmentTest
atest WifiDppQrCodeScannerFragmentTest
atest WifiNetworkListFragmentTest
atest WifiDppChooseSavedWifiNetworkFragmentTest
Change-Id: I1d44eeb3bdc7bfb2ec2e4d81efaab64b066651ad
9d33313735