commit_or_abort can be used with low level dao

The code pattern handled by commit_or_abort is every where in the dao with
the exception of overridding the exception with a new one.

With this modification, old code will be able to use the context manager without
rewritting consumer code
use commit_or_abort everywhere

use the context manager commit_or_abort where session begin,end are
used
use add_me and add_me_all in all test cases
remove useless package test_preriquisites
remove useless test module that test sqlalchemy sessions
Merge branch 'master' into session-interface-cleanup

Conflicts:
	xivo_dao/data_handler/queue_members/dao.py
	xivo_dao/helpers/db_utils.py
Merge branch 'session-interface-cleanup'