Add check in case there ISN'T any update

Added an extra check to flag an error if there is no current update timestamp because the host has, for example, been built from an internet source and has already got up to date packages and no updates have yet successfully run.

agents/plugins/yum

@@ -111,17 +111,24 @@ then
     fi
 
     # Check last time of installed Updates from yum history
-	# Added "list all" to the history command as in situations where 20 or more RPM installs have been completed (non updates
-	# yum commands) have been run, the script will incorrectly report that the server has never updated
-	# Yum only lists 20 of the last actions when using only the "history" command.
+    # Added "list all" to the history command as in situations where 20 or more RPM installs have been completed (non updates
+    # yum commands) have been run, the script will incorrectly report that the server has never updated
+    # Yum only lists 20 of the last actions when using only the "history" command.
 
     # Switch command based on which Major version we are running
     if [ "$MAJOR_VERSION" -ge 8 ]; then
-	
-	    LAST_UPDATE_TIMESTAMP=$(/usr/bin/yum -C --quiet --noplugins history list | awk '{if(NR>2)print}' | grep  ' U \|Upgrade\|Update' | cut -d '|' -f3  | head -n 1 | date -f - +"%s" || echo "-1")
+
+        LAST_UPDATE_TIMESTAMP=$(/usr/bin/yum -C --quiet --noplugins history list | awk '{if(NR>2)print}' | grep  ' U \|Upgrade\|Update' | cut -d '|' -f3  | head -n 1 | date -f - +"%s" || echo "-1")
     else
-	    LAST_UPDATE_TIMESTAMP=$(/usr/bin/yum -C --quiet --noplugins history list all| awk '{if(NR>2)print}' | grep  ' U \|Upgrade\|Update' | cut -d '|' -f3  | head -n 1 | date -f - +"%s" || echo "-1")
-	fi
+        LAST_UPDATE_TIMESTAMP=$(/usr/bin/yum -C --quiet --noplugins history list all| awk '{if(NR>2)print}' | grep  ' U \|Upgrade\|Update' | cut -d '|' -f3  | head -n 1 | date -f - +"%s" || echo "-1")
+    fi
+    # Add check in case this is a brand new built machine that has had
+    # up to date pacakges installed during build. In this case, neither
+    # command above will have yielded a value and LAST_UPDATE_TIMESTAMP
+    # will be empty
+
+    if [ "$LAST_UPDATE_TIMESTAMP" == "" ]; then LAST_UPDATE_TIMESTAMP=-1; fi
+
 
     echo $BOOT_REQUIRED
     echo $UPDATES