Fix map.clear() usage for array type maps

Fix map.clear() usage for array type maps

Calling delete on an array type map entry does not have an effect.
Instead, the entry needs to be zeroed out, since the array slot always
exists. To avoid unnecessary calls to update(), only call update() when
the map type is array-like. The type was not exposed to python up until
now, so add it.

Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>