ovsdb-server: Add and remove databases during run time.

The commit allows a user to add a database file to a
ovsdb-server during run time. One can also remove a
database file from ovsdb-server's control.

Feature #14595.
Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Co-authored-by: Ben Pfaff <blp@nicira.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>
ofp-errors: Fix typos in error enumeration names.

OFPGMFC is so nice these constants said it twice.

Signed-off-by: Ben Pfaff <blp@nicira.com>