bpo-11063: Create _uuid1 submodule

[vstinner]

uuid module: move getnode() and uuid1() implementations to a new
_uuid1 submodule which is now loaded on demand to reduce side effects
on "import uuid".

https://bugs.python.org/issue11063

[vstinner]

_unixdll_getnode() and _windll_getnode() functions used UUID(bytes=bytes).node to convert bytes to a UUID object, then to get the node. I added a new "def _bytes_to_node(rawbytes):" helper function to break the dependency from _uuid1 to the uuid.UUID class. IMHO _bytes_to_node() is simple enough to justify the "duplication" of the code.

[gronke]

@Haypo have you noticed #3684 ? You're addressing a similar problem and your comment's are welcome! Personally I don't see a benefit from breaking uuid in two separate files. Instead we could move all code paths involved in uuid1() together. I'll comment on the other PR why we didn't.

[vstinner]

Abandonned in favor of @pitrou's PR #3796.