[BUG] Support creating mars Series using dict with mars tensor as values

**Describe the bug**
The Series executing result is not expected when passing dict as below:
``` Python

In [23]: r = mt.random.rand(10).sum()

In [24]: md.Series({'a':r, 'b':r}).execute()
Out[24]:
a Tensor(op=TensorSum, shape=())
b Tensor(op=TensorSum, shape=())
dtype: object

```

Start by running the reported md.Series({'a': r, 'b': r}).execute() reproduction with a Mars tensor value, then trace the Series construction path for dictionaries. Done means the executed Series contains the computed scalar results rather than Tensor objects; no source file or test is named in the issue.

Written by the indexing model from the issue text.