Add is_ubuntu function

This replaces all of the [[ "$os_PACKAGE" = "deb" ]] tests, except when
those tests are before straight calls to dpkg.

Change-Id: I8a3ebf1b1bc5a55d736f9258d5ba1d24dabf04ea
diff --git a/tools/info.sh b/tools/info.sh
index a872d59..583a994 100755
--- a/tools/info.sh
+++ b/tools/info.sh
@@ -88,7 +88,7 @@
 # - We are going to check packages only for the services needed.
 # - We are parsing the packages files and detecting metadatas.
 
-if [[ "$os_PACKAGE" = "deb" ]]; then
+if is_ubuntu; then
     PKG_DIR=$FILES/apts
 else
     PKG_DIR=$FILES/rpms