middleware.sizelimit: stop importing wsgi

This patches stops the sizelimit module to rely on the deprecated WSGI
module.

Change-Id: Ie804a74f833112f7d6d30f787f426d6f7ad0be2f
Remove extension_stubs

This file isn't used anywhere, let's get rid of it.

Change-Id: I13a1c81616697af2baa659ea6033061b2951602c
Enables db2 server disconnects to be handled pessimistically

A checkout listener can be added to sqlalchemy to be able to
handle database disconnect pessimistically and avoid an error in
the event of a DB restart or simply a temp connection issue due
to network glitches. At the moment only mysql is enabled with
this feature. This patch enables db2 as well.

Partial-Bug: #1231657
Change-Id: I5563360b43c4b648f5b035099b0e1d2e71d32503
Make _extra_keys a property of ModelBase

Currently  _get_extra_keys() used as as function.
Changing it to read only property makes class interface more cleaner
and reliable
We don't have to explicitly call it and it can't be accidently overriden
by assigning of an instance variable

Change-Id: I236408be953f299854fce80aa38e24708c13a60a
Remove start index 0 in range()

Remove the useless arg ("start index" = 0) in files, since its default
value is 0, to make code cleaner.

Fixes bug #1259744

Change-Id: I02fc3d96cacdbae1be9e9283362bb87518d97a7c
Merge "Enables db2 server disconnects to be handled pessimistically"
Merge "middleware.sizelimit: stop importing wsgi"
Merge "Remove extension_stubs"
Merge "Make _extra_keys a property of ModelBase"
Merge "Remove start index 0 in range()"