pbTests: Increase QPC.sh sleep time

[Willsparker]

Ref: #2121

Debian10/aarch64 doesn't have enough time to boot in 120 seconds, however it was able to after 180s.

Checklist

• commit message has one of the standard prefixes
• FAQ.md updated if appropriate
• other documentation is changed or added (if applicable)
• playbook changes run through VPC or QPC (if you have access)
• for inventory.yml changes, bastillion/nagios/jenkins updated accordingly

[sxa]

Given we're up to three minutes just now I'd prefer to see something that checks every 10-15 seconds to see if it's sufficiently "up" but I'm ok with this as an intermediate solution