Add option to source configuration from a file

Add option to source configuration from a file

If the configfile:// schema is used, the data is sourced from an ini
style config file instead of being read from a database.

The tables in this data source will be considered read-only and
all modification functions will throw exceptions.

Only 2 and 3 columns tables are supported, and the first column
values must not contain spaces (typically a name/identifier).

The adminconfig db is the only supported one at this time.

Signed-off-by: Simo Sorce <simo@redhat.com>
Reviewed-by: Patrick Uiterwijk <puiterwijk@redhat.com>