## What changes were proposed in this pull request?
Image test seems failed in Python 3.6.0 / NumPy 1.13.3. I manually tested as below:
```
======================================================================
ERROR: test_read_images (pyspark.ml.tests.ImageReaderTest)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/.../spark/python/pyspark/ml/tests.py", line 1831, in test_read_images
self.assertEqual(ImageSchema.toImage(array, origin=first_row[0]), first_row)
File "/.../spark/python/pyspark/ml/image.py", line 149, in toImage
data = bytearray(array.astype(dtype=np.uint8).ravel())
TypeError: only integer scalar arrays can be converted to a scalar index
----------------------------------------------------------------------
Ran 1 test in 7.606s
```
To be clear, I think the error seems from NumPy - 75b2d5d427/numpy/core/src/multiarray/number.c (L947)
For a smaller scope:
```python
>>> import numpy as np
>>> bytearray(np.array([1]).astype(dtype=np.uint8))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: only integer scalar arrays can be converted to a scalar index
```
In Python 2.7 / NumPy 1.13.1, it prints:
```
bytearray(b'\x01')
```
So, here, I simply worked around it by converting it to bytes as below:
```python
>>> bytearray(np.array([1]).astype(dtype=np.uint8).tobytes())
bytearray(b'\x01')
```
Also, while looking into it again, I realised few arguments could be quite confusing, for example, `Row` that needs some specific attributes and `numpy.ndarray`. I added few type checking and added some tests accordingly. So, it shows an error message as below:
```
TypeError: array argument should be numpy.ndarray; however, it got [<class 'str'>].
```
## How was this patch tested?
Manually tested with `./python/run-tests`.
And also:
```
PYSPARK_PYTHON=python3 SPARK_TESTING=1 bin/pyspark pyspark.ml.tests ImageReaderTest
```
Author: hyukjinkwon <gurwls223@gmail.com>
Closes#19835 from HyukjinKwon/SPARK-21866-followup.
92cfbeeb5c