[hotfix] run healthchecks in parallel and restart on fail

• bug: healthchecks hang and then stop running
• possible causes:
  • the sequence fails and never completes when one healtcheck times out and/or gets an untrusted fingerprint
  • the failure is in a thunk inside a sequence call and therefore never gets caught
• fixes:
  • use Promise.all
  • catch a failed launchHealthchecksJob and relaunch if it ever fails
  • provide slightly more resilient logging in logger.error