Fixing connected tests with SiteStore mock.

[develric]

This is a companion PR for PRthis FluxC and should fix connected tests linked to SiteStore being not mockable.

To test:

Should be enough to trigger optional UI tests and check it's all green.

Regression Notes

1. Potential unintended areas of impact
   N/A

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   N/A

3. What automated tests I added (or what prevented me from doing so)
   N/A

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading the APK here.

[planarvoid]

Thanks for the changes! Feel free to merge this once you update the fluxC tag