Prevent abusing the GH API

On large deployments with many jobs, we cannot check each job that
we recorded in the DB against the GH API.

Before this change, if a job was updated more than 10 minutes ago,
garm would check against the GH api if that job still existed. While
this approach allowed us to maintain a consistent view over which jobs
still exist and which are stale, it had the potential of spamming the
GH API, leading to rate limiting.

This change uses the scale-down loop as an indicator for job staleness.

If a job remains in queued state in our DB, but has dissapeared from GH
or was serviced by another runner and we never got the hook (garm was down
or GH had an issue - happened in the past), then garm will spin up a new
runner for it. If that runner or any other runner is scaled down, we check
if we have jobs in the queue that should have matched that runner. If we did,
there is a high chance that the job no longer exists in GH and we can remove
the job from the queue.

Of course, there is a chance that GH is having issues and the job is never
pushed to the runner, but we can't really account for everything. In this case
I'd rather avoid rate limiting ourselves.

Signed-off-by: Gabriel Adrian Samfira <gsamfira@cloudbasesolutions.com>

params/params.go

@@ -297,6 +297,20 @@ func (p *Pool) PoolType() PoolType {
 	return ""
 }
 
+func (p *Pool) HasRequiredLabels(set []string) bool {
+	asMap := make(map[string]struct{}, len(p.Tags))
+	for _, t := range p.Tags {
+		asMap[t.Name] = struct{}{}
+	}
+
+	for _, l := range set {
+		if _, ok := asMap[l]; !ok {
+			return false
+		}
+	}
+	return true
+}
+
 // used by swagger client generated code
 type Pools []Pool