Fix Early Use of die function in stack.sh
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

openstack-dev/devstack,openstack-dev/devstack,nawawi/openstack,nawawi/openstack