Fix for trying to access session after closing in /metrics #52

Job	Run time
Generate SRPMS (f40)	1m 34s
Generate SRPMS (f41)	1m 20s
Build bodhi-client on f40 in Koji	10m 30s
Build bodhi-client on f41 in Koji	12m 42s
Build bodhi-messages on f40 in Koji	11m 39s
Build bodhi-messages on f41 in Koji	11m 33s
Build bodhi-server on f40 in Koji	14m 54s
Build bodhi-server on f41 in Koji	14m 29s
	1h 18m 41s

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