Better SIGINT handling for CASD

Description

Ensures we don't kill buildbox-casd when sending SIGINT to BuildStream.

Sending SIGINT to BuildStream is entirely normal and expected and we handle it. We should prevent it from reaching buildbox-casd though otherwise the process would get killed and we would not be able to continue building.

Fix #1120 (closed)

approved this merge request

assigned to @marge-bot123

added 4 commits

• ec785fe7...2516668b - 2 commits from branch master
• 2b9e6f5b - cascache.py: Block SIGINT in the buildbox-casd process
• 5615bb4d - cascache.py: Block SIGINT in the CasUsageMonitor process

Compare with previous version

merged

mentioned in commit f886d33a