Return a dict of available instances sizes (a.k.a machine types) and
    convert them to something more serializable.

def avail_sizes(conn=None):
    '''
    Return a dict of available instances sizes (a.k.a machine types) and
    convert them to something more serializable.
    '''
    if not conn:
        conn = get_conn()
    raw_sizes = conn.list_sizes('all')  # get *all* the machine types!
    sizes = []
    for size in raw_sizes:
        zone = size.extra['zone']
        size.extra['zone'] = {}
        size.extra['zone'].update(zone.__dict__)
        mtype = {}
        mtype.update(size.__dict__)
        sizes.append(mtype)
    return sizes