creating the rpmrepo metadata

This includes two method for build rpm repo:
  1. create the metadata in rootfs_rpm
  2. standalone binary for building the metadata

Not both of them are needed, generally #2 fits more for the purpose,
but #1 may have its use on rootfs creation using zypper.

Both share some problems and are subjected for future improvement:
  1. the createrepo now builds metadata for the whole directory,
     if there are more than one arch, it builds for all, which means
     rootfs_rpm may run longer if more builds have been run.
  2. createrepo builds metadata for stale rpms

Signed-off-by: Qing He <qing.he@intel.com>

meta/classes/rootfs_rpm.bbclass

@@ -11,6 +11,9 @@ do_rootfs[depends] += "rpm-native:do_populate_sysroot"
 # Needed for update-alternatives
 do_rootfs[depends] += "opkg-native:do_populate_sysroot"
 
+# Creating the repo info in do_rootfs
+do_rootfs[depends] += "createrepo-native:do_populate_sysroot"
+
 do_rootfs[recrdeptask] += "do_package_write_rpm"
 
 AWKPOSTINSTSCRIPT = "${POKYBASE}/scripts/rootfs_rpm-extract-postinst.awk"
@@ -38,6 +41,8 @@ fakeroot rootfs_rpm_do_rootfs () {
 
 	${RPM_PREPROCESS_COMMANDS}
 
+	createrepo "${DEPLOY_DIR_RPM}"
+
 	# Setup base system configuration
 	mkdir -p ${IMAGE_ROOTFS}/etc/rpm/