rootfs_rpm.bbclass: save rpmlib rather than remove it

The rpmlib was removed when images that add
"remove_packaging_data_files" to ROOTFS_POSTPROCESS_COMMAND, which would
make the increment rpm image generation doesn't work in the second
build, since list_installed_packages would get incorrect value in the
second build, move the rpmlib to ${T} rather than remove it, and move it
back when INC_RPM_IMAGE_GEN =1.

[YOCTO #2690]

(From OE-Core rev: c30e79510c06701f10f659eedaa0fe785538ac17)

(From OE-Core rev: 15e13ea1fc8a0c29b4ca68c31c83ca013c89c36e)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Elizabeth Flanagan <elizabeth.flanagan@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/image.bbclass

@@ -143,6 +143,12 @@ fakeroot do_rootfs () {
     # When use the rpm incremental image generation, don't remove the rootfs
     if [ "${INC_RPM_IMAGE_GEN}" != "1" -o "${IMAGE_PKGTYPE}" != "rpm" ]; then
         rm -rf ${IMAGE_ROOTFS}
+    elif [ -d ${T}/saved_rpmlib/var/lib/rpm ]; then
+        # Move the rpmlib back
+        if [ ! -d ${IMAGE_ROOTFS}/var/lib/rpm ]; then
+                mkdir -p ${IMAGE_ROOTFS}/var/lib/
+                mv ${T}/saved_rpmlib/var/lib/rpm ${IMAGE_ROOTFS}/var/lib/
+        fi
     fi
 	rm -rf ${MULTILIB_TEMP_ROOTFS}
 	mkdir -p ${IMAGE_ROOTFS}