Change cfn-signal option --exit to --exit-code
Change cfn-signal option --exit to --exit-code

According cfn user guide, the long option of cfn-signal -e should be
--exit-code.

Fixes bug #1220080

Change-Id: Id4e9feefd387a744f5e933aa4e9ea8a6f6f02a7c

bbandaru/heat-cfntools,openstack/heat-cfntools