Add the node_reboot_required metric to yum.sh (#165)

Added the node_reboot_required metric to yum.sh, based on PR #70,
with the requested changes incorporated in the code

Signed-off-by: Arnaud Vazard <vaz-git@gmx.com>

yum.sh

@@ -3,7 +3,7 @@
 # Description: Expose metrics from yum updates.
 #
 # Author: Slawomir Gonet <slawek@otwiera.cz>
-# 
+#
 # Based on apt.sh by Ben Kochie <superq@gmail.com>
 
 set -u -o pipefail
@@ -37,3 +37,14 @@ if [[ -n "${upgrades}" ]] ; then
 else
   echo 'yum_upgrades_pending{origin=""} 0'
 fi
+
+# If yum-utils/dnf-utils is not installed then we skip rendering this metric
+if [[ -x /bin/needs-restarting ]] ; then
+  echo '# HELP node_reboot_required Node reboot is required for software updates.'
+  echo '# TYPE node_reboot_required gauge'
+  if /bin/needs-restarting -r  > /dev/null 2>&1 ; then
+    echo 'node_reboot_required 0'
+  else
+    echo 'node_reboot_required 1'
+  fi
+fi