Description of Problem / Feature Request

cmd/clair/main.go installs a signal handler (SIGINT only) to perform a graceful shutdown.
I don't think this is working as desired

Expected Outcome

I would have expected HTTP servers to stop accepting new connections, then a short grace period for in-flight requests to complete (exiting as soon as no requests are in flight), as a last resort terminating connections then exiting if any are still running when the grace period expires.

Actual Outcome

HTTP servers are shutdown immediately, with any in-flight HTTP requests being severed.

Recreate:

1. start a local Postgres
2. run a clair indexer locally:
   go run ./cmd/clair/ -conf ./local-dev/clair/config-frostmar-local.yaml -mode indexer
3. start a long-running HTTP request, eg an indexing operation
   curl -H "Content-Type: application/json" http://localhost:6060/indexer/api/v1/index_report -d ...<snipped>...
4. send SIGINT - [CTRL+C] the go run command, or kill -INT <pid>
   => logs output gracefully shutting down component=main signal=interrupt
   => process immediately exits
   => curl request immediately gives error curl: (52) Empty reply from server

I'd hope to see:
=> logs to output gracefully shutting down component=main signal=interrupt
=> 10 sec grace-period timeout
=> process exits only after the grace period
=> logs to output unregistered signal handler
=> curl to fail with an error response

Environment

Running locally on a Mac

• Clair version/image: git tag v4.7.2
• Clair client name/version: curl
• Host OS: MacOS
• Kernel (e.g. uname -a):
• Kubernetes version (use kubectl version): n/a
• Network/Firewall setup: n/a