Add emulators/qemu-utils

qemu-utils is a new port which installs a few miscellaneous qemu utilities
that are useful even without emulation capabilities. It is useful where
emulation is not needed, because it has far fewer dependencies than qemu.
It is equivalent to the Debian package of the same name.

Reviewed by: sbruno, brd
Approved by: brd (ports)
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D8038