fixed a bug in the test for propagating map exceptions
fixed a bug in the test for propagating map exceptions

A too-broad except clause caused the test to always pass by trapping the assertion error designed to trigger test failure.

JioCloud/stevedore,mandeepdhami/stevedore,citrix-openstack-build/stevedore,openstack/stevedore,JioCloud/stevedore,varunarya10/stevedore,nelsnelson/stevedore,citrix-openstack-build/stevedore,varunarya10/stevedore,nelsnelson/stevedore,mandeepdhami/stevedore