send an ssh key as vm-disk intial payload. use the MAGIC string as a filename to allow for older boot2docker.iso's
replace shelling out to tar with archive/tar
`./boot2docker config` outputs current cfg, and tells the user where the profile file is

this will also allow them to make an intial cfg file to modify
Merge pull request #92 from SvenDowideit/boot2docker-config

Boot2docker config
Merge pull request #94 from SvenDowideit/add-ssh-keys

send an ssh key as vm-disk intial payload.