shell: enable hostside test: testAllCharacterDevicesAreSecure

Enable shell to have access to /dev for running the
world accessable mode test on /dev.

This approach adds shell to the list of excluded domains
on neverallows around chr_files, but locks down the access
for shell to only getattr.

It was done this lightly more complicated way to prevent
loosening the allow rules so that any domain would have
getattr permissions.

Change-Id: Idab466fa226ddbf004fcb1bbcaf98c8326605253