Add fstyp(8). This utility, named after its SVR4 counterpart, detects
filesystems. It differs from file(1) in that it gives machine-parseable
output, it outputs filesystem labels, doesn't get confused by other
formats metadata, and runs in Capsicum sandbox.

Differential Revision: https://reviews.freebsd.org/D1255
Relnotes: yes
Sponsored by: The FreeBSD Foundation