wireproto: use pushkey.encodekey

pushkey: introduce an ``encodekeys`` function This function provides a standardized way to exchange pushkey content over the wire.

bundle2: add more phase movement in the test To test phase exchange with bundle2 we need some phase movement to happen. Appropriate logging is added to track those changes.

bundle2: use non-publishing repo in test If we are going to test usage of bundle for phases exchange, we need some phase movements to be exchanged.

bundle2: use a smarter template for test We use a more compact template that includes phase information.

getbundle: declare type of parameters In addition to listing the expected options for ``getbundle``, we also list their types and handle the encoding/decoding automatically. This should make it easier for extensions to transmit additional information to getbundle.

bundle2: introduce a ``caps20to10`` function This function factors the creation of appropriate entries to use in ``bundlecaps`` argument of ``getbundle``. This cleans up code calling ``getbundle`` and helps its usage in more part of the code.

bundle2: introduce a bundle2caps function The process of decoding remote bundle2caps blob into a dictionary is cumbersome. We move it into a small helper function. This will clarify code that reads bundle2 capabilities of peers and helps using it in new places.

exchange: reinsert comment in the right place Unrelated new code was inserted between the original comment and the related code block.

docker: check for docker.io first