Don't convert numeric protocol values to int

They are treated as strings everywhere. Converting them to int causes problems
when using postgresql as the database backend because it doesn't automatically
cast them back to integer.

Change-Id: I9f0a5149d24a4c003409728e50376569c97e7325
Closes-bug: 1330490
(cherry picked from commit 3be62f878e8165cf3bce357a00b8a583773f7d3b)
Merge "Don't convert numeric protocol values to int" into stable/icehouse
Merge branch 'stable/icehouse' of https://github.com/openstack/quantum into stable/icehouse