Add connection services (cs).

Add a special pipe call to cs to use plan 9 pipes. This
fails opening the pipe.

Add tests/common, an ndb file cs uses; add commands to makefile
to copy it when fill-kfs target is used.

Now we're hitting a very nasty problem due to our 2-level fds.

cs opens a pipe and gets the fd, which is 6, but the plan 9 fd is 0.
cs opens #s/cs and wants to write the fd of the pipe to it, and
writes 6. #s barfs because that's not a valid fd -- the valid fd
is 0.

For now, srv will do the translation from akaros to plan 9 fd, but this
is getting increasingly nasty.

Clean up pipe a bit.

To test:
ash ifconfig
cs [-f /lib/ndb/common]
the optional argument should not be needed ;-)
Note it fails on the pipe. All other bits seem to work, but once
I added the pipes, that part won't work.

Signed-off-by: Ronald G. Minnich <rminnich@google.com>