File streams handling improvement for oc-azure-storage-adapter

[pbazydlo]

Implementing workaround/hack for the private/public file permissions (described in #61) have had a side effect when putting file content when content is provided as a stream.

After we have written the stream to private container, the stream is at its end. I have not been able to figure out how to reset this stream to beginning for writes to public container, I've tried the following:

• use fs.read with empty buffer, read length of 0 and position set to 0 in an attempt to reset the stream
  • this had no effect on stream whatsoever
• pipe through azure write stream
  • as one could expect azure write stream is not pass-through, so any further reads would basically hang

In order to be able to write the actual content to public container after using up original stream with file content, I set up additional stream from azure private container to azure public container. Even though it puts ugly and unnecessary strain on the network I opted in to do this because:

• I couldn't solve original issue
• I did not want to load files into memory, that would put unnecessary memory pressure on registry and I think it could potentially block event loop

How to resolve this issue

Figure out a way to either:
a) Solve #61
b) Reset the stream to it's beginning so that it can be reused