Fix Add Import action by using go list to suggest import paths

[marwan-at-work]

Fixes #258

[gopherbot]

This PR (HEAD: 17b0c21) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/vscode-go/+/240001 to see it.

Tip: You can toggle comments from me using the comments slash command (e.g. /comments off)
See the Wiki page for more info

[gopherbot]

Message from Rebecca Stambler:

Patch Set 1:

(1 comment)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/240001.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Marwan Sulaiman:

Patch Set 1:

(1 comment)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/240001.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Rebecca Stambler:

Patch Set 1:

(1 comment)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/240001.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

This PR (HEAD: 9e05bfd) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/vscode-go/+/240001 to see it.

Tip: You can toggle comments from me using the comments slash command (e.g. /comments off)
See the Wiki page for more info

[gopherbot]

Message from Marwan Sulaiman:

Patch Set 2:

(1 comment)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/240001.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Hyang-Ah Hana Kim:

Patch Set 2:

(3 comments)

I observed this CL caused multiple test failures - https://github.com/golang/vscode-go/pull/259/checks?check_run_id=809087856

Looking into a bit, go list all triggered from the "test listPackages" test, for example, failed with errors like

'can't load package: package github.com/uudashr/gopkgs: code in directory /Users/hakim/go/src/github.com/uudashr/gopkgs expects import "github.com/uudashr/gopkgs/v2"
can't load package: package github.com/uudashr/gopkgs/internal: code in directory /Users/hakim/go/src/github.com/uudashr/gopkgs/internal expects import "github.com/uudashr/gopkgs/v2/internal"
can't load package: package test/testfixture/importTest: found packages main (cgoImports.go) and hello (groupImports.go) in /Users/hakim/go/src/test/testfixture/importTest'

The detailed errors may vary depending on what's under the current GOPATH directory, but it seems like go list all is more sensitive to what's currently under GOPATH.

Rebecca, have you seen errors like this when working with go list for gopls?
Another question is the version compatibility - is go list working well with earlier versions of go (prior to go1.13)?

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/240001.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Hyang-Ah Hana Kim:

Patch Set 2:

(2 comments)

Ok, I think I figured out why promises didn't seem to resolve.

Still various tests are failing

• Replace vendor packages with relative path
• all tests related to Completion.

Would be nice if you can investigate the test failures. Thanks!

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/240001.
After addressing review feedback, remember to publish your drafts!

[hyangah]

@marwan-at-work I think this PR is obsolete. Can we close this?

[marwan-at-work]

Yep! Closing it now. Thanks for the ping 🏓