Fix TypeError being thrown by six.reraise in Engine Package Loader.
Fix TypeError being thrown by six.reraise in Engine Package Loader.

Currently, six.reraise throws a TypeError in Python 3.4, because
it is being called incorrectly in function load_package in
package_loader.ApiPackageLoader.

The way six.reraise is called was changed to reflect the
"generic" way it is called throughout the rest of the file.

Closes-Bug: #1632107

Change-Id: Iadb9c5a6483bf779afd916ebe53852b72581b03e

openstack/murano,openstack/murano