This removes personality extension, as well as the rebuild extension
point for servers.
We add an operation flag to translate extension because personality
extension uses different kwarg names depending on the operation. This
is done with a set of constants which should prevent typos silently
causing failures.
A few variables are renamed in servers.py to avoid multiline
statements.
Part of bp:api-no-more-extensions
Change-Id: I47deae0279f85d9a355d1248b6e90af732406514
76b58b8f89