cloudinit: merge cloudconfig info from user-data and meta-data

This attempts to retrieve cloudconfigs from two sources: the meta-data
service, and the user-data service. If only one cloudconfig is found,
that is applied to the system. If both services return a cloudconfig,
the two are merged into a single cloudconfig which is then applied to
the system.

Only a subset of parameters are merged (because the meta-data service
currently only partially populates a cloudconfig). In the event of any
conflicts, parameters in the user-data cloudconfig take precedence over
those in the meta-data cloudconfig.

test

@@ -18,7 +18,7 @@ declare -a TESTPKGS=(initialize system datasource pkg network)
 if [ -z "$PKG" ]; then
 	GOFMTPATH="$TESTPKGS coreos-cloudinit.go"
 	# prepend repo path to each package
-	TESTPKGS=${TESTPKGS[@]/#/${REPO_PATH}/}
+	TESTPKGS="${TESTPKGS[@]/#/${REPO_PATH}/} ./"
 else
 	GOFMTPATH="$TESTPKGS"
 	# strip out slashes and dots from PKG=./foo/