Port contrib/netbsd-tests/fs/h_funcs.subr to FreeBSD

Use kldstat -m to determine whether or not a filesystem is loaded. This works
well with tmpfs, ufs, and zfs

MFC after:	1 month
Sponsored by:	Dell EMC Isilon

contrib/netbsd-tests/fs/h_funcs.subr

@@ -45,6 +45,15 @@ require_fs() {
 
 	# if we have autoloadable modules, just assume the file system
 	atf_require_prog sysctl
+	# Begin FreeBSD
+	if true; then
+		if kldstat -m ${name}; then
+			found=yes
+		else
+			found=no
+		fi
+	else
+	# End FreeBSD
 	autoload=$(sysctl -n kern.module.autoload)
 	[ "${autoload}" = "1" ] && return 0
 
@@ -57,6 +66,9 @@ require_fs() {
 		fi
 		shift
 	done
+	# Begin FreeBSD
+	fi
+	# End FreeBSD
 	[ ${found} = yes ] || \
 		atf_skip "The kernel does not include support the " \
 		         "\`${name}' file system"