Fix Early Use of die function in stack.sh

This commit fixes use of die function before it's defined.
die function can be used after sourcing $TOP_DIR/functions chain-
sources $TOP_DIR/functions-common.
Because fixed portion of stack.sh checks existence of $TOP_DIR/inc
and sourcing $TOP_DIR/function chain source $TOP_DIR/inc, this commit
uses echo & exit command instead of die function.

Closes-Bug: #1913021
Change-Id: I5ec174cf7b02269525b1bfd0bfa94ea889d16fce
diff --git a/stack.sh b/stack.sh
index 036afd7..c334159 100755
--- a/stack.sh
+++ b/stack.sh
@@ -96,19 +96,25 @@
 # templates and other useful files in the ``files`` subdirectory
 FILES=$TOP_DIR/files
 if [ ! -d $FILES ]; then
-    die $LINENO "missing devstack/files"
+    set +o xtrace
+    echo "missing devstack/files"
+    exit 1
 fi
 
 # ``stack.sh`` keeps function libraries here
 # Make sure ``$TOP_DIR/inc`` directory is present
 if [ ! -d $TOP_DIR/inc ]; then
-    die $LINENO "missing devstack/inc"
+    set +o xtrace
+    echo "missing devstack/inc"
+    exit 1
 fi
 
 # ``stack.sh`` keeps project libraries here
 # Make sure ``$TOP_DIR/lib`` directory is present
 if [ ! -d $TOP_DIR/lib ]; then
-    die $LINENO "missing devstack/lib"
+    set +o xtrace
+    echo "missing devstack/lib"
+    exit 1
 fi
 
 # Check if run in POSIX shell