Add is_fedora and exit_distro_not_supported functions

Between is_fedora, is_ubuntu and is_suse, we can make the code a bit
simpler to read. We also use exit_distro_not_supported to identify
places where we need implementation details for new distros.

As "/sbin/service --skip-redirect" is Fedora-specific, guard this with a
is_fedora test too.

Change-Id: Ic77c0697ed9be0dbb5df8e73da93463e76025f0c
diff --git a/tools/info.sh b/tools/info.sh
index 583a994..f01dbea 100755
--- a/tools/info.sh
+++ b/tools/info.sh
@@ -90,15 +90,19 @@
 
 if is_ubuntu; then
     PKG_DIR=$FILES/apts
-else
+elif is_fedora; then
     PKG_DIR=$FILES/rpms
+else
+    exit_distro_not_supported "list of packages"
 fi
 
 for p in $(get_packages $PKG_DIR); do
     if [[ "$os_PACKAGE" = "deb" ]]; then
         ver=$(dpkg -s $p 2>/dev/null | grep '^Version: ' | cut -d' ' -f2)
-    else
+    elif [[ "$os_PACKAGE" = "rpm" ]]; then
         ver=$(rpm -q --queryformat "%{VERSION}-%{RELEASE}\n" $p)
+    else
+        exit_distro_not_supported "finding version of a package"
     fi
     echo "pkg|${p}|${ver}"
 done