Use oslo's execute() and ssh_execute() methods

Based on nova's Ice9cdbdc5f3e5a9f8365f5d99acf1863a9fe3e7a

This patch also PEP8-fy the imports from common/utils

Change-Id: I71f08e892e438ce998c1c80d15c0c6a287112d66
Sync some db changes from Oslo

Import two new db exception classes, and
sync many changes to openstack.common.db.sqlalchemy:
- models.py has better py3 support
- updated / deprecated option names in session.py
- many new functions available in utils.py

Change-Id: Ia7bac4ea61dbb8cb5baf6cf2064a94895cba3f2c
Do not allow API to expose error stacktrace

Due to specific implementation of RPC error deserialization we have
remote exception traceback built into the error message, therefore
web server puts it to the response and sends to the client. This
patch adds Pecan hook that cuts off traceback from the error message
before it sent to the client.

Closes-Bug: #1244747
Change-Id: Ic12f151123f4ccce36d64608873eeb99eccc525a
Merge "Sync some db changes from Oslo"
Merge "Use oslo's execute() and ssh_execute() methods"