Upgrading to GitLab Mattermost in GitLab 8.9

Same thing here. Panic looks like this:

2016-06-23_15:11:53.39476 main.main()
2016-06-23_15:11:53.39476       /var/lib/jenkins/jobs/mattermost-platform-release/workspace/src/github.com/mattermost/platform/mattermost.go:104 +0x9c9
2016-06-23_15:11:55.05863 panic: Failed to open sql connection pq: the database system is starting up
2016-06-23_15:11:55.05867
2016-06-23_15:11:55.05868 goroutine 1 [running]:
2016-06-23_15:11:55.05868 panic(0xb8dd80, 0xc8202dd300)
2016-06-23_15:11:55.05869       /usr/local/go/src/runtime/panic.go:481 +0x3e6
2016-06-23_15:11:55.05869 github.com/mattermost/platform/store.setupConnection(0xdb97c0, 0x6, 0xc820135d80, 0x8, 0xc82004efc0, 0x5d, 0xa, 0xa, 0xc8202dcf00, 0x10)
2016-06-23_15:11:55.05870       /var/lib/jenkins/jobs/mattermost-platform-release/workspace/src/github.com/mattermost/platform/store/sql_store.go:218 +0x894
2016-06-23_15:11:55.05871 github.com/mattermost/platform/store.initConnection(0x41da0f)
2016-06-23_15:11:55.05871       /var/lib/jenkins/jobs/mattermost-platform-release/workspace/src/github.com/mattermost/platform/store/sql_store.go:63 +0x11b
2016-06-23_15:11:55.05872 github.com/mattermost/platform/store.NewSqlStore(0x0, 0x0)
2016-06-23_15:11:55.05872       /var/lib/jenkins/jobs/mattermost-platform-release/workspace/src/github.com/mattermost/platform/store/sql_store.go:85 +0x49
2016-06-23_15:11:55.05873 github.com/mattermost/platform/api.NewServer()
2016-06-23_15:11:55.05874       /var/lib/jenkins/jobs/mattermost-platform-release/workspace/src/github.com/mattermost/platform/api/server.go:36 +0xe8
2016-06-23_15:11:55.05874 main.main()
2016-06-23_15:11:55.05875       /var/lib/jenkins/jobs/mattermost-platform-release/workspace/src/github.com/mattermost/platform/mattermost.go:104 +0x9c9
2016-06-23_15:19:52.39029 panic: Failed to open sql connection pq: the database system is starting up
2016-06-23_15:19:52.39128
2016-06-23_15:19:52.39129 goroutine 1 [running]:
2016-06-23_15:19:52.39129 panic(0xb8dd80, 0xc82040b480)
2016-06-23_15:19:52.39129       /usr/local/go/src/runtime/panic.go:481 +0x3e6
2016-06-23_15:19:52.39130 github.com/mattermost/platform/store.setupConnection(0xdb97c0, 0x6, 0xc82012dd78, 0x8, 0xc82004f020, 0x5d, 0xa, 0xa, 0xc82040ae00, 0x10)
2016-06-23_15:19:52.39130       /var/lib/jenkins/jobs/mattermost-platform-release/workspace/src/github.com/mattermost/platform/store/sql_store.go:218 +0x894

Is this due to the failed upgrade?

I also tried a clean install and that doesn't work at all either.

In my opinion, the whole point of the "omnibus" is that you should be able to turn on Mattermost on a clean installed new system (that has never run a pre-8.9 gitlab) and have it WORK.