ovsdb: add support for role-based access controls

ovsdb: add support for role-based access controls

Add suport for ovsdb RBAC (role-based access control). This includes:

   - Support for "RBAC_Role" table. A db schema containing a table
     by this name will enable role-based access controls using
     this table for RBAC role configuration.

     The "RBAC_Role" table has one row per role, with each row having a
     "name" column (role name) and a "permissions" column (map of
     table name to UUID of row in separate permission table.) The
     permission table has one row per access control configuration,
     with the following columns:
          "name"          - name of table to which this row applies
          "authorization" - set of column names and column:key pairs
                            to be compared against client ID to
                            determine authorization status
          "insert_delete" - boolean, true if insertions and
                            authorized deletions are allowed.
          "update"        - Set of columns and column:key pairs for
                            which authorized updates are allowed.
   - Support for a new "role" column in the remote configuration
     table.
   - Logic for applying the RBAC role and permission tables, in
     combination with session role from the remote connection table
     and client id, to determine whether operations modifying database
     contents should be permitted.
   - Support for specifying RBAC role string as a command-line option
     to ovsdb-tool (Ben Pfaff).

Signed-off-by: Lance Richardson <lrichard@redhat.com>
Co-authored-by: Ben Pfaff <blp@ovn.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>