Test tensor execution in distributed mode about mars

[qinxuye]

If most failures are due to the serialization, maybe we need to enhance the tests in tensor/expressions.

The e2e tests are quite heavy, I think we only need to test on some special and corner cases.

[wjsi]

We may test under a mimic setting for the distributed cases in an actor-free environment. That is,

1. Serialize / deserialize the tensor graph;
2. Tile with the same code as GraphActor used;
3. Extract operands by get_executable_operand_dag;
4. Execute operands one by one.

[qinxuye]

This issue would be replaced by #267 , close first.