Avoid using "raise" to reraise with modified exception

The code changes the exception and reraises it.
This commit changes the code to use the same way as
excutils.save_and_reraise_exception does to ensure
the exception context.

This is the last patch of reraise clean up series.

Closes-Bug: #1279813
Change-Id: I8787dcbdc8321f75964de26e97cae395707aafc2
Merge "Avoid using "raise" to reraise with modified exception"