Do not raise NEW exceptions

Raising NEW exception is bad practice, because we lose TraceBack.
So all places like:

except SomeException as e:
    raise e

should be replaced by

except SomeException:
    raise

If we are doing some other actions before reraising we should
store information about exception then do all actions and then
reraise it. This is caused by eventlet bug. It lost information
about exception if it switch threads.

fixes bug 1191730

Change-Id: Id4aaadde7e69f0bc087cf6d96bb041d53feb131d
Update to use OSLO db

This code implements the blueprint oslo-db-support

NOTES:
1. The new section is database (this is backward compatible
   with DATABASE)
2. The sql_* are deprecated. They are also backward compatible.
3. Eventlets DB pool is no longer supported

Change-Id: I6fa7c3817f6a5d8bef48382e0e754b88521f2289
Merge "Do not raise NEW exceptions"
Merge "Update to use OSLO db"
Add gre tunneling support for the ML2 plugin

This patch add the type_driver GRE to enable teh creation of GRE
tunnels with the OVS agent

Change-Id: I1a33a4bd3ebc4c97eecf17a59ce16b8c2066ec66
Implements: blueprint ml2-gre