Re-raise python exception correctly

[Petr Jediný]

try:
    ...
except Exception as e:
    raise e

will create new stack trace on python 2 we should re-raise with raise only

try:
    ...
except Exception as e:
    raise

as described in http://www.ianbicking.org/blog/2007/09/re-raising-exceptions.html

[OpenContrail Admin (ci-admin-f)]

Review in progress for https://review.opencontrail.org/36759
Submitter: Petr Jedin? (<email address hidden>)

[OpenContrail Admin (ci-admin-f)]

Reviewed: https://review.opencontrail.org/36759
Committed: http://github.com/Juniper/contrail-controller/commit/97e052715a5023bfba1b558c861b6f4bf873cccf
Submitter: Zuul (<email address hidden>)
Branch: master

commit 97e052715a5023bfba1b558c861b6f4bf873cccf
Author: Petr Jediný <email address hidden>
Date: Tue Oct 24 14:29:32 2017 +0200

Re-raise exception correctly

Change-Id: I079b703227bdf134932a81cd4606146ddae32141
Closes-Bug: #1726846