Eliminate gratuitous DB difference vs Nova

Looks like this was an abritrary cleanup done as part of the import. It
conflicts with a more recent change in Nova.

We can move to using try_import() once we've killed the Nova copy
of this code.

Change-Id: I5c67d3fbd846a262feb724e26b14447a76561ae6
Remove duplicate DB options

sql_dbpool_enable and sql_connection_trace are declared twice.

Looks like this was a merge conflict when sql_dbpool_enable changed
from int to bool.

Change-Id: I553c5beea916e0ee296648342324fd53167c073a
Be explicit about set_default() parameters

We probably only want to support people using set_defaults() for a
limited set of config options, so explicitly list those as parameters
to the method. This is what we do for rpc and log options too.

Change-Id: I3bfc5355e82eec17480b9547662e847dc0d74138
Merge "Eliminate gratuitous DB difference vs Nova"
Merge "Remove duplicate DB options"
Merge "Be explicit about set_default() parameters"