Setting Host part of address url to :authority pseudo header

[everpeace]

fixes #1566

What I've changed

This PR sets custom :authority pseudo header with Host part of address url via grpc.WithAuthority dial option.

This is because:

• grpc-go uses a slightly different naming scheme(https://github.com/grpc/grpc/blob/master/doc/naming.md)
• This will end up setting rfc non-complient :authority header to address string (e.g. tcp://127.0.0.1:1234)
  • valid authority header does not contain a scheme https://tools.ietf.org/html/rfc3986#section-3.2

I think current --addr option uses net.URL even though custom connection helpers like kube-pod://, dockercontainer://. So, I think that taking url.Host part wouldn't cause a serial problem.

[tonistiigi]

@AkihiroSuda wdyt?

If this is better then why isn't it the default in go-grpc?

[everpeace]

@tonistiigi @AkihiroSuda I posted #1620 in another approach to fix the issue. Another one doesn't contain any breaking changes. How about it?

[everpeace]

@AkihiroSuda oh, thanks for your approval. I'm closing another PR. Thanks.

[everpeace]

@tonistiigi @AkihiroSuda Could you kindly merge this PR? Are there any concern about this PR?

[edrevo]

A question about how this change propagates: does this change affect the dockerfile frontend or does it affect the buildkit code? I'm asking in order to understand if I need to wait for a new release of buildkit and then wait until that release gets integrated into docker, or if I can just # syntax = docker/dockerfile:N as soon as version N gets released in order to get this fix.