Fix add_backend user handling.
Fix add_backend user handling.

We need to make sure that the user dict is updated before validating.
The same stands for removing the backend after checking that libcloud
cannot connect.

afivos/mist.io,kelonye/mist.io,Lao-liu/mist.io,afivos/mist.io,munkiat/mist.io,munkiat/mist.io,Lao-liu/mist.io,zBMNForks/mist.io,munkiat/mist.io,afivos/mist.io,johnnyWalnut/mist.io,Lao-liu/mist.io,DimensionDataCBUSydney/mist.io,johnnyWalnut/mist.io,kelonye/mist.io,zBMNForks/mist.io,munkiat/mist.io,DimensionDataCBUSydney/mist.io,DimensionDataCBUSydney/mist.io,johnnyWalnut/mist.io,Lao-liu/mist.io,DimensionDataCBUSydney/mist.io,kelonye/mist.io,zBMNForks/mist.io