Add a timestamp to the log output for better diagnosis

when we are looking at logs generated by the gate jobs
we need timestamps on the output of stack.sh so we can
figure out what was being executed around the time when
there was a problem in say nova-network

Change-Id: I203e8dae97715d6ee46a4088c7577b9be66cf09d

stack.sh

@@ -598,7 +598,15 @@ if [[ -n "$LOGFILE" ]]; then
     exec 3>&1
     if [[ "$VERBOSE" == "True" ]]; then
         # Redirect stdout/stderr to tee to write the log file
-        exec 1> >( tee "${LOGFILE}" ) 2>&1
+        exec 1> >( awk '
+                {
+                    cmd ="date +\"%Y-%m-%d %H:%M:%S \""
+                    cmd | getline now
+                    close("date +\"%Y-%m-%d %H:%M:%S \"")
+                    sub(/^/, now)
+                    print
+                    fflush()
+                }' | tee "${LOGFILE}" ) 2>&1
         # Set up a second fd for output
         exec 6> >( tee "${SUMFILE}" )
     else