XDG_CACHE_HOME can't work for create new emulator

[Bin Li]

I create a new directory to save the download ubuntuimages. so that each user could use the same image without download it by each user.

When I try to create a new emulator, it will download the ubuntuimages.

sudo ubuntu-emulator create ubuntu --arch=i386 --channel=ubuntu-touch/ubuntu-rtm/14.09

After that I create a directory '/home/emulator/' and change the permission so that everyone can visit. Then change the environment like below.

export XDG_CACHE_HOME /home/emulator/

After that when I create a new emulator called ubuntu2, I found it will download the same ubuntuimages again in .cache/ubuntuimages/

sudo ubuntu-emulator create ubuntu2 --arch=i386 --channel=ubuntu-touch/ubuntu-rtm/14.09

Thanks!