HostedUI uses cached configuration

[tjleing]

Describe the bug
HostedUI configuration is loaded from SharedPreferences even when awsconfiguration.json is updated more recently. This can manifest in a verification error on one of the initialization fields, even after changing the config file.

To Reproduce

1. Set up app with Hosted UI.
2. Set a breakpoint on _showSignIn in AWSMobileClient.java, run the app and note that it uses the proper configuration blob.
3. Update the awsconfiguration.json (and amplifyconfiguration.json -- you can run grep to make sure that there is no possible other source of backups), changing the WebDomain, for example.
4. Re-run the app and note that the blob has not updated.
5. Delete the virtual device and create a new one.
6. Re-run the app and note that the blob has updated.

Which AWS service(s) are affected?
After looking through AWSMobileClient.java (search for mStore.get), it looks like the issue is just with Hosted UI.

Expected behavior
Hosted UI should load the proper configuration from awsconfiguration.json and trust it over the SharedPreferences configuration. I expect that this will just be a reordering of getHostedUIJSON(awsConfig).

[banji180]

After following the steps above, I can see the updated change in the config used by the HostedUI.