test: add e2e tests for certificate revocation (#1345)

## Summary

- Add end-to-end tests for certificate revocation functionality
- Test that a revoked client certificate cannot connect to the VPN
- Test that a new certificate can be created with the same name as a
revoked one (validating the fix from #1185)
- Test that the new certificate can successfully connect

## Test Flow

1. **Initial connectivity tests** - existing tests pass
2. **Certificate revocation test**:
   - Create a new client `revoketest`
   - Connect with the certificate (verifies it works)
   - Disconnect the client
   - Revoke the certificate via the install script
- Try to reconnect with revoked cert (verifies connection is rejected)
3. **Reuse revoked name test**:
   - Create a new certificate with the same name `revoketest`
   - Verify both revoked and valid entries exist in `index.txt`
   - Connect with the new certificate (verifies it works)

## Changes

| File | Changes |
|------|---------|
| `test/server-entrypoint.sh` | Start OpenVPN in background, add
revocation test orchestration |
| `test/client-entrypoint.sh` | Add revocation test phases with signal
file coordination |
| `docker-compose.yml` | Remove read-only restriction on shared volume
for client |
| `Makefile` | Increase timeout from 60 to 180 iterations |
| `.github/workflows/docker-test.yml` | Increase timeouts, fix shared
volume |

Makefile

@@ -3,7 +3,7 @@
 # Run the full test suite
 test: test-build test-up
 	@echo "Waiting for tests to complete..."
-	@for i in $$(seq 1 60); do \
+	@for i in $$(seq 1 180); do \
 		if docker logs openvpn-client 2>&1 | grep -q "ALL TESTS PASSED"; then \
 			echo "✓ Tests passed!"; \
 			$(MAKE) test-down; \
@@ -15,7 +15,7 @@ test: test-build test-up
 			$(MAKE) test-down; \
 			exit 1; \
 		fi; \
-		echo "Waiting... ($$i/60)"; \
+		echo "Waiting... ($$i/180)"; \
 		sleep 2; \
 	done; \
 	echo "Timeout waiting for tests"; \