IL-719 Fix issues with Terraform state locking and stale processes

[thomashashi]

See https://support.instruqt.com/support/tickets/137 --- we can no longer rely on Instruqt to stop all shell tab processes as you move from one challenge to another, which causes two problems with this track: 1) users sometimes check whilst a Terraform command is still running, which causes subsequent confusion when they run terraform again and get error messages about the state being locked; 2) We tell users to start blast-radius, which may be running when we tell them later on to start it again, and they get port already in use errors.

• Where we run terraform commands in a challege, ensure in the check script that Terraform is no longer running
• After we tell users to start blast-radius, but do not tell them to stop it, but rely on it not running later, use a challenge cleanup script to stop it
• Make some checks a bit more robust
• Fix some Bash quoting errors which could lead to silent failures
• Slight clarification on some instructions

[thomashashi]

Leaving as WIP until I ran run test suite and also get at least one independent person to run through the WIP version successfully