nanobsd: Prefer nano_umount to umount

nano_umount[^1] is a convenience routine used to override issues with
umount(8) without changing the nanobsd.sh source code.  There were a few
places where it was not being used.

[^1]: Introduced in 6d12b61a88 ("Add a routine for easy workaround any
umount issues w/o hacking nanobsd.sh.")

Reviewed by:	imp, emaste
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D48780

tools/tools/nanobsd/defaults.sh

@@ -812,7 +812,7 @@ cust_pkgng() {
 	mount -t nullfs -o noatime -o ro ${NANO_PACKAGE_DIR} ${NANO_WORLDDIR}/_.p
 	mount -t devfs devfs ${NANO_WORLDDIR}/dev
 
-	trap "umount ${NANO_WORLDDIR}/dev; umount ${NANO_WORLDDIR}/_.p ; rm -xrf ${NANO_WORLDDIR}/_.p" 1 2 15 EXIT
+	trap "nano_umount ${NANO_WORLDDIR}/dev; nano_umount ${NANO_WORLDDIR}/_.p ; rm -xrf ${NANO_WORLDDIR}/_.p" 1 2 15 EXIT
 
 	# Install pkg-* package
 	CR "${PKGCMD} add /_.p/${_NANO_PKG_PACKAGE}"
@@ -837,8 +837,8 @@ cust_pkgng() {
 	CR0 "${PKGCMD} info"
 
 	trap - 1 2 15 EXIT
-	umount ${NANO_WORLDDIR}/dev
-	umount ${NANO_WORLDDIR}/_.p
+	nano_umount ${NANO_WORLDDIR}/dev
+	nano_umount ${NANO_WORLDDIR}/_.p
 	rm -xrf ${NANO_WORLDDIR}/_.p
 }
 

tools/tools/nanobsd/legacy.sh

@@ -113,7 +113,7 @@ create_code_slice() {
 			-y ${NANO_HEADS}`
 	fi
 
-	trap "echo 'Running exit trap code' ; df -i ${MNT} ; umount ${MNT} || true ; mdconfig -d -u $MD" 1 2 15 EXIT
+	trap "echo 'Running exit trap code' ; df -i ${MNT} ; nano_umount ${MNT} || true ; mdconfig -d -u $MD" 1 2 15 EXIT
 
 	gpart create -s bsd "${MD}"
 	gpart add -t freebsd-ufs -b 16 "${MD}"