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 #2440]
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>
