Support building gotests for distribution in $GOROOT/misc/akaros/mnt

Also includes support script on the akaros side for grabbing them and
extracting them from the mount
No need to copy the cpio file, and abstract port number out
Update when getting the src for the 9pserver
Don't delete the contents of the mntdir by default
Change default port to 5555 and copy all scripts from akaros-bin
Push the 'exit' call into the rpc call, not distributed throughout