I purchased an iPad Air 2 at an auction and it too was supervisor locked(OTA controlled)
It also had a standard passcode (which I didn't know)
I accidentally stumbled on a way to bypass the supervisor thing.
I updated to iOS 9.2.1. I did a restore & update through itunes.
I was greeted by a message "such & such company will configure your ipad".
When it finished configuring it had an overlay screen that only allowed reminders/notes.
I couldn't access any of the icons. They were hidden/locked under the company's custom interface.
You could see the regular desktop flash for just a second then immediately it was covered by the company's custom interface.
I did another restore & update.
***IMPORTANT PART***
I created a 3rd page for desktop icons and dragged the settings icon to the newly created page.
When it booted I went through all the standard setup stuff (wifi, enable location, etc.) then when the supervised over the air configuration started I let it finish.
Right as it was getting ready to change to the locked company overlay I turned off my wifi.
I was then able to access the standard desktop, icons, etc.
I set a restrictions passcode and disabled notes, reminders, and calendar.
I ran a backup then rebooted and turned on wifi.
I played around for a 10 minutes or so then shut it down & rebooted again.
Everything works as it should.
I am able to access it in itunes, add music, photos, etc.
It no longer warns me that it is supervised by another computer.
The supervisor security info is still there in the settings/general section.
Kind of a goofy, lucky way I stumbled onto.
It's fully functional now.