Print the function stack on param error in testlib

Most of the functions of the test library include some type of
parameter validation, when a function is called and one of its
parameters don't comply with the expected parameters it terminates
the whole script. This is expected, but sometimes it can be
difficult to figure out what was the function that received the
incorrect parameters in the script.

This commit adds a function that prints a stack of the function
calls so when a script is terminated it is easier to figure out
the culprit.

test/functional/testlib.bash

@@ -58,6 +58,18 @@ generate_random_name() {
 
 }
 
+print_stack() {
+
+	echo "An error occurred"
+	echo "Function stack (most recent on top):"
+	for func in ${FUNCNAME[*]}; do
+		if [ "$func" != "print_stack" ] && [ "$func" != "terminate" ]; then
+			echo -e "\\t$func"
+		fi
+	done
+
+}
+
 terminate() {
 
 	# since the library could be sourced and run from an interactive shell
@@ -67,8 +79,10 @@ terminate() {
 	local msg=$1
 	local param
 	case "$-" in
-		*i*)	: ${param:?"$msg, exiting..."} ;;
-		*)		echo "$msg, exiting..."
+		*i*)	print_stack
+				: "${param:?"$msg, exiting..."}" ;;
+		*)		print_stack
+				echo "$msg, exiting..."
 				exit 1;;
 	esac