wic: Add option to not change fstab

Create an option to wic doesn't change fstab file, the final
fstab file will be same that in rootfs and wic doesn't update
file, e.g adding a new mount point.

Users can control the fstab file content in base-files recipe.
This is useful if you want to only create an partition but not
add fstab mount point or add new mount point using label e.g:

LABEL=recovery /recovery auto defaults 0  1

(From OE-Core rev: 00420ec42140c1b752132bda190dede85756d157)

Signed-off-by: Fabio Berton <fabio.berton@ossystems.com.br>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/wic/plugins/imager/direct.py

@@ -71,6 +71,7 @@ class DirectPlugin(ImagerPlugin):
         self.outdir = options.outdir
         self.compressor = options.compressor
         self.bmap = options.bmap
+        self.no_fstab_update = options.no_fstab_update
 
         self.name = "%s-%s" % (os.path.splitext(os.path.basename(wks_file))[0],
                                strftime("%Y%m%d%H%M"))
@@ -165,7 +166,10 @@ class DirectPlugin(ImagerPlugin):
         filesystems from the artifacts directly and combine them into
         a partitioned image.
         """
-        new_rootfs = self._write_fstab(self.rootfs_dir.get("ROOTFS_DIR"))
+        if self.no_fstab_update:
+            new_rootfs = None
+        else:
+            new_rootfs = self._write_fstab(self.rootfs_dir.get("ROOTFS_DIR"))
         if new_rootfs:
             # rootfs was copied to update fstab
             self.rootfs_dir['ROOTFS_DIR'] = new_rootfs