multi_del
批量删除一个hashkey下的多条sortkey数据
def multi_del(self, hash_key, sortkey_set, timeout=0):
"""
Remove multiple entire <hash_key, sort_key>-values in pegasus.
:param hash_key: (str) which hash key used for this API.
:param sortkey_set: (set) sort keys in set.
:param timeout: (int) how long will the operation timeout in milliseconds.
if timeout > 0, it is a timeout value for current operation,
else the timeout value specified to create the instance will be used.
:return: (tuple<error_types.code.value, int>) (code, count).
code: error_types.ERR_OK.value when data got succeed.
count: count of deleted k-v pairs.
"""