Add non-verbose output mode

Set VERBOSE=False to turn off the noise of stack.sh output.  All
output still is written to the logfile if LOGFILE is set.

Rebased

Change-Id: I316bc4d68c997ec907a48e720e2f7778428d935b
diff --git a/lib/heat b/lib/heat
index 0b234c4..e713b39 100644
--- a/lib/heat
+++ b/lib/heat
@@ -15,9 +15,9 @@
 # stop_XXX
 # cleanup_XXX
 
-# Print the commands being run so that we can see the command that triggers
-# an error.  It is also useful for following along as the install occurs.
-set -o xtrace
+# Save trace setting
+XTRACE=$(set +o | grep xtrace)
+set +o xtrace
 
 
 # Defaults
@@ -178,3 +178,6 @@
     # This function intentionally left blank
     :
 }
+
+# Restore xtrace
+$XTRACE