wic: do not overwrite autogenerated /etc/fstab with original too early

DirectImageCreator.__write_fstab() generates new /etc/fstab in sysroot
with rootfs contents. The fstab entries are generated base on the
initialn contents of /etc/fstab, plus any extra (other than / or
/boot) partitions listed in *.wks. A backup of original /etc/fstab is
done in a temp location. Subsequent call to __restore_fstab() restores
the backup copy, replacing the autogenerated one.

Calling __restore_fstab() before Wic_PartData.prepare() brings back the
original fstab before the partition image file actually is created. As
such, the autogenerated /etc/fstab will not make it to the partition.

(From OE-Core rev: a9e59d7b1fa1ed33ce9678fb77a367800d7a8f87)

Signed-off-by: Maciej Borzecki <maciej.borzecki@open-rnd.pl>
Signed-off-by: Maciek Borzecki <maciek.borzecki@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/mic/imager/direct.py

@@ -270,10 +270,12 @@ class DirectImageCreator(BaseImageCreator):
             # when/if we need to actually do package selection we
             # should modify things to use those objects, but for now
             # we can avoid that.
+
+            fstab = self.__write_fstab(self.rootfs_dir.get("ROOTFS_DIR"))
+
             p.prepare(self, self.workdir, self.oe_builddir, self.rootfs_dir,
                       self.bootimg_dir, self.kernel_dir, self.native_sysroot)
 
-            fstab = self.__write_fstab(p.get_rootfs())
             self._restore_fstab(fstab)
 
             self.__instimage.add_partition(int(p.size),
@@ -286,6 +288,7 @@ class DirectImageCreator(BaseImageCreator):
                                            boot = p.active,
                                            align = p.align,
                                            part_type = p.part_type)
+
         self.__instimage.layout_partitions(self._ptable_format)
 
         self.__imgdir = self.workdir