VPN-6706: fix timer after server unavailable

[mcleinman]

Description

If a connection attempt results in a "server unavailable" modal, the user is encouraged to select a new server. However, that results in the timer being stuck at 0:00:00:

1. Since the first server never fully connected, the timer is never started
2. Since the second server is technically a server switch, the timer isn't touched when switching servers

Since this could be fragile, I added a test to make sure this doesn't break in the future. While writing that test:

• forceServerUnavailable got some parameters added to it, as the CLI command requires parameters (previously, this testing command was unused)
• I changed the stub server response to have different "public keys". We gray out unavailable servers based on their public key - so when we marked a server unavailable in our test, all servers were being marked unavailable because they shared a public key.
• I created a new helper function to prevent code duplication.

Reference

VPN-6706

Checklist

• My code follows the style guidelines for this project
• I have not added any packages that contain high risk or unknown licenses (GPL, LGPL, MPL, etc. consult with DevOps if in question)
• I have performed a self review of my own code
• I have commented my code PARTICULARLY in hard to understand areas
• I have added thorough tests where needed