Fix six.reraise bug in rbac_rule_validation

This PS fixes an issue [0] when calling six.reraise in
rbac_rule_validation after a generic Exception has been
caught. Instead of using six.reraise and changing the
exception's detailed error message unnecessarily,
excutils.save_and_reraise_exception from oslo_utils
is used instead.

[0] http://logs.openstack.org/97/507697/5/check/legacy-tempest-dsvm-patrole-member/d2530aa/job-output.txt.gz#_2017-11-02_20_04_35_107548

Change-Id: I99f2cc60f301172847dd8f98fbc7deff4d5e94e4
2 files changed