Ok something very weird is going on. Initially I was able to mount ios 7.0.4 with no problems. Then for some reason it just stopped mounting and got into that infinite trust loop like OP has. Then I tried installing and reinstalling libimobiledevice libraries(libimobiledevice3, libimobiledevice4, libimobiledevice-dev, libimobiledevice-utils) with no luck and something in between got corrupted because after rebooting I was not able to login into the desktop. And as far as I can say, thankfully, because it forced me to purge and reinstall ubuntu-desktop and compiz. I simply presed ctrl+alt+f1 and did the following
After following through this I managed to login to desktop, then plugged in my ipad and for a change got an error: "Unhandled Lockdown error (-20)". After that the device did not disappear from the list and I just clicked it from nautillus sidebar and everything mounted automatically...
sudo service lightdm stop
sudo apt-get purge ubuntu-desktop* unity* compiz* compiz-* -y
sudo rm -vfr compiz* compiz-*
sudo apt-get install ubuntu-desktop unity compiz
sudo service lightdm start
Not sure if it will work for others, but it did work for my configuration and in my particular situation.