Hi there,
a few months ago I wanted to speed up the upgrade precedure of minor release upgrades, so I wrote a script for it.
I wanted to share it for quite some time, but didn't get around to actually doing that. @it33 reminded me that it would be a good idea 
I put it into a gist: https://gist.github.com/reach3r/faed21778269a21a353eced9a7051b7d
Example usage: ./mattermost_upgrade.sh 3.4.0
As of now the script has some limitations:
- it does not backup the database
- it is only useful for minor updates; major releases that require manual user actions can not be handled correctly
These limitations stem from my scenario, where a database backup is not necessary. I might get around to implementing it at some point, but obviously everyone is welcome to improve the script .
Have a nice day!