crbuild fixes

I had some trouble getting the build working:

First vm-setup.sh had a problem with sudo, as it ignored the /etc/sudoers.d/crbuild file because the permissions where set the 0644 instead of 0440.

There was also an error on about the user not accepting the EULA of the package: ttf-mscorefonts-installer.
After I ran sudo sh -c "echo ttf-mscorefonts-installer msttcorefonts/accepted-mscorefonts-eula select true | debconf-set-selections" it worked.
I haven't tested reinstalling the whole VM, so I'm not a 100% sure if it really works out of the box now, but I don't see why not.

vm-build.sh: Ubuntu does no longer link /bin/sh to bash, so the scripts ran with /bin/dash (notice the _d_ instead of _b_) instead of /bin/bash which caused some problems in the android build tools (it couldn't find envsetup_functions.sh).

vm-build.sh looked for .build_android instead of .build_arm as stated in the instructions.

I also added a default value for CPUS so one could run ./vm-build.sh without specifying any environment variables first.