We refactor a bunch of methods to support re-using an open connection
when available. There's some code in the connection manager to support
nesting connections to avoid deadlocks when we call a method that can
open a connection while we already have a connection checked out - but
it might be better in the long run if we just got better at passing open
connections around whenever possible.
Add a helper method on the base db broker class to make it easier to
write methods that can optionally take an existing connection.
Change-Id: Ifd54d76ab1a5a9d82848f3cae89c3e53134aa129
2e321d94ed