Improvements to Docker file #3486

Job	Run time
check_branch	1s
Check if database upgrade tests should be run	4s
Build Openfire from source (17, zulu)	26m 49s
Build Openfire from source (21, zulu)	22m 59s
Build (and maybe push) Docker image	8m 20s
Execute aioxmpp-based CI tests	1m 52s
Generate DEB artifact	1m 48s
Test MySQL Upgrades	1m 25s
Execute Connectivity CI tests	28s
Test Postgres Upgrades	53s
Execute Smack-based CI tests	55s
Test SQL Server Upgrades	1m 10s
Check if Docker Hub secrets exist	1s
Publish to Maven	0s
Publish to Docker Hub	0s
Test tagged images published to Docker Hub	0s
	1h 6m 45s

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