Configurable db plugins

I'd like to propose the ability to support configurable db plugins for
trove. Currently the sqlalchemy api's configure_db() function in trove
supports the ability to pass in 1 or more db plugin (mappers) classes
[1] which allow consumers to add their own schema (tables) to trove's
db. However the current trove.cmd.*.py entry points do not support any
means to pass in such plugins (example [2]).

I was thinking something like the following:
(a) Support a comma list property on CONF.DEFAULT in the trove conf
files.. e.g.
[DEFAULT]
db_plugins =
org.foo.bar.sqlalchemy.BarPlugins,org.yadda.sqlalchemy.MyPlugins

(b) In the trove CONF, default the comma list property to empty list
(e.g. []).

(c) Update each of the respective trove.cmd.*.py entry point (main()
methods) which call into configure_db() to first load any plugin classes
and them pass them into the method.. e.g.
get_db_api().configure_db(CONF, import_classes(CONF.db_plugins))

The above should give consumers the ability to plug into the trove
database api and add scheme without upstream changes.

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