CI: run mage with "-v" to not discard output, and move mage to a submodule

[thaJeztah]

travis: run mage with -v to not discard output

Before this:

$ go run mage.go lint
Error: running "/Users/sebastiaan/go/bin/golangci-lint run ./..." failed with exit code 1
exit status 1

$ go run mage.go test
Error: running "go test -race -v ./..." failed with exit code 1
exit status 1

After this:

$ go run mage.go -v lint
Running target: Lint
exec: /Users/sebastiaan/go/bin/golangci-lint run ./...
entry.go:89:6: `iamNotUsed` is unused (deadcode)
func iamNotUsed() {
     ^
Error: running "/Users/sebastiaan/go/bin/golangci-lint run ./..." failed with exit code 1
exit status 1

$ go run mage.go -v test
Running target: Test
exec: go test -race -v ./...
=== RUN   TestRegister
...
?   	github.com/sirupsen/logrus/internal/testutils	[no test files]
FAIL
Error: running "go test -race -v ./..." failed with exit code 1
exit status 1

move "mage" to a separate module

Move the magefile related files to a submodule, so that it does not become a dependency for logrus itself.

[thaJeztah]

@dgsb PTAL

Wondering; perhaps we should move to GitHub actions, now that travis-ci.org is shutting down (and there's ready-made actions for Golang and Golang-ci-lint). Looking at the magefile, it's only doing some minimal things, which could be handled by some standard GH actions.

(I'll try to prepare a PR for that for consideration)

[dgsb]

@thaJeztah thanks, that's a clever trick.

Regarding github action I'd rather not move things out from the magefile, the purpose is to get independant as much as possible from the CI system whatever it is so that any migration when needed is seamless.

[thaJeztah]

Regarding github action I'd rather not move things out from the magefile, the purpose is to get independant as much as possible from the CI system whatever it is so that any migration when needed is seamless.

Got distracted by other pull requests I was working on, but I opened #1239 to look at / discuss what GH Actions could look like 🤗