Changes implement 2 new flags --sse-customer-key and
--sse-copy-source-customer-key that can be used by user to
provide a key for server side encryption.

Once these options are set extra headers are added to request
accordingly to SSE-C specification [1]

We also ensure that object_get respects provided extra_headers

This PR squashes and rebases on current master changes
implemented by @jheller

[1] https://docs.aws.amazon.com/AmazonS3/latest/userguide/specifying-s3-c-encryption.html

In order to test out server-side encryption we need to use secure connection
fisrt. This way we generate self-signed certificates for minio.

With this commit we reflect on the review process and improve code
and testing process.