Junk deploy builds stack up if the current deploy gets stuck

Create a deployment whose deploy script randomly either finishes in five seconds or hangs for an hour. Schedule a trigger to kick off the deploys every five minutes.

Actual: When the first hanging deploy (call it "deploy-1") is running, deploy-2, deploy-3, deploy-4, etc. will stack up. When deploy-1 is finally finished, deploy-12 will kick off and run to completion. At that point, even though there are no currently running deploys, the stacked up deployments (deploy-2, deploy-3 ... deploy-11) will all still say that they're "Waiting" but their moment will never come.

Expected: Don't trigger a deployment while a deployment is currently running. The only deployment after deploy-1 should be deploy-2, even if deploy-1 takes an hour.

Apropos https://support.atlassian.com/servicedesk/customer/portal/10/BSP-16092