bsdinstall: mount is not needed for the ZFS install case

Because the datasets are already mounted by zfsboot, and the mount script
doesn't know anything about ZFS. Also do not execute the "umount" script for
ZFS for the same reasons.

Reviewed by:		dteske, tsoome
Sponsored by:		Citrix Systems R&D
MFC after:		1 week
Differential revision:	https://reviews.freebsd.org/D10738

usr.sbin/bsdinstall/scripts/script

@@ -42,6 +42,11 @@ f_include $BSDCFG_SHARE/variable.subr
 # DISTRIBUTIONS
 # BSDINSTALL_DISTDIR
 
+#
+# Default name of the ZFS boot-pool
+#
+: ${ZFSBOOT_POOL_NAME:=zroot}
+
 ############################################################ GLOBALS
 
 #
@@ -53,8 +58,6 @@ msg_installation_error="Installation Error!"
 
 error()
 {
-	[ -f "$PATH_FSTAB" ] && bsdinstall umount
-	
 	local file
 	f_getvar "$VAR_DEBUG_FILE#+" file
 	if [ "$file" ]; then
@@ -63,6 +66,13 @@ error()
 		# No need to restore title, pining for the fjords
 	fi
 
+	[ -f "$PATH_FSTAB" ] || exit
+	if [ "$ZFSBOOT_DISKS" ]; then
+		zpool export $ZFSBOOT_POOL_NAME
+	else
+		bsdinstall umount
+	fi
+
 	exit 1
 }
 
@@ -99,8 +109,8 @@ if [ "$ZFSBOOT_DISKS" ]; then
 	bsdinstall zfsboot
 else
 	bsdinstall scriptedpart "$PARTITIONS"
+	bsdinstall mount
 fi
-bsdinstall mount
 
 # Unpack distributions
 bsdinstall checksum
@@ -125,7 +135,11 @@ if [ -f /tmp/bsdinstall-installscript-ab ]; then
 fi
 
 bsdinstall entropy
-bsdinstall umount
+if [ "$ZFSBOOT_DISKS" ]; then
+	zpool export $ZFSBOOT_POOL_NAME
+else
+	bsdinstall umount
+fi
 
 f_dprintf "Installation Completed at %s" "$( date )"