Cleanup fcntl(3) usage and fd lifetimes in vmd(8).

Cleanup fcntl(3) usage and fd lifetimes in vmd(8).

Remove extraneous fcntl(3) usage for setting fd features that can
be set at time of open(2), pipe2(2), or socketpair(2). Also cleans
up pty creation switching to using functions from libutil instead
of direct ioctl(2) calls.

ok mlarkin@, original diff ok claudio@ as well.