fix BinaryData inconsistencies and also make it accept any packable

[erickvermot]

currently BinaryData has many inconsistencies, like not initializing with a False object, but accepting it on its pack method:

In [1]: from pyof.foundation.basic_types import BinaryData
In [2]: BinaryData([])
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-2-170088959e05> in <module>()
----> 1 BinaryData([])
python-openflow/pyof/foundation/basic_types.py in __init__(self, value)
    423         """
    424         if not isinstance(value, bytes):
--> 425             raise ValueError('BinaryData must contain bytes.')
    426         super().__init__(value)
    427 

ValueError: BinaryData must contain bytes.

In [3]: BinaryData().pack([])
Out[3]: b''

Or not accepting None in initialization:

In [4]: BinaryData(None)
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-4-6b71433feedd> in <module>()
----> 1 BinaryData(None)

python-openflow/pyof/foundation/basic_types.py in __init__(self, value)
    423         """
    424         if not isinstance(value, bytes):
--> 425             raise ValueError('BinaryData must contain bytes.')
    426         super().__init__(value)
    427 

ValueError: BinaryData must contain bytes.

Furthermore, any packable object can become a BinaryData, so I see no reason not to accept it as value. This can be very useful, like for accepting unknown structures like in the optional HelloMessage body.

Many of these fixes were implemented in #392, but since the PR was rejected I am separating them in other PRs.