This replaces all usage of `protoc` with `buf`. See `tools/buf/README.md` for more.

Despite being a security release for Go, we do not believe Nomad is
impacted.

1.15.5 is due in a couple days but we may release before then.

Dockerhub is going to rate limit unauthenticated pulls.

Use our HashiCorp internal mirror for builds run through CircleCI.
Co-authored-by: Mahmood Ali <mahmood@hashicorp.com>

Currently we compile (but don't run) the e2e tests as part of `test-other`,
which is skipped for branches named `e2e-*`. Move this check into the
`test-e2e` job. Split out the vault compatibility integration check as its own
makefile target for clarity.

We currently have two jobs commented out in ENT because we don't have the test
target configured there. So having the filter attached to one of those jobs
means changes to filters always create a merge conflict.

Branches for the e2e code base can't have impact on the unit tests, so running
those tests just extends the time it takes to ship e2e updates. This changeset
updates the CircleCI config so that e2e branches run linting, build the
binary, and run the e2e unit tests (currently just vault compatibility).

Upgrade to golang 1.15

Starting with golang 1.5, setting Ctty value result in `Setctty set but Ctty not valid in child` error, as part of https://github.com/golang/go/issues/29458 .
This commit lifts the fix in https://github.com/creack/pty/pull/97 .

Go 1.14.7 fixes CVE-2020-16845 which is not believed to impact Nomad.

Pick up fixes [golang 1.14.6 bug fixes](https://github.com/golang/go/issues?q=milestone%3AGo1.14.6+label%3ACherryPickApproved), specially the one where reflect.DeepEqual returns true even if values don't match, affecting our tests integrity.

Go 1.14.4 contains two CVEs which are fixed in 1.14.5:

 - [CVE-2020-15586](https://golang.org/issue/34902)
 - [CVE-2020-14039](https://golang.org/issue/39360)

Upon consideration with HashiCorp security these CVEs are considered low
severity for Nomad and no new security fix binary will be released.

Avoid running algolia job in forks or enterprise private repositories

This is extracted from #8094, where I have run into some snags. Since
these ESLint fixes aren’t actually connected to the Ember 3.16 update
but involve changes to many files, we might as well address them
separately. Where possible I fixed the problems but in cases where
a fix seemed too involved, I added per-line or -file exceptions.

These are used by release process, so add them to CI to notice if we
break release scripts.

This PR switches the Nomad repository from using govendor to Go modules
for managing dependencies. Aspects of the Nomad workflow remain pretty
much the same. The usual Makefile targets should continue to work as
they always did. The API submodule simply defers to the parent Nomad
version on the repository, keeping the semantics of API versioning that
currently exists.

Mostly to ease conflict resolution with Enterprise fork, as Enterprise
CI doesn't support windows.

Always install go and vault: the check may accidentally use the CircleCI
pre-installed go version instead of the cached version.

Also, always install from sources without caching.  Go/vault
installation is basically a tarball download.  That's equivalent to
CirleCI caching without the complexity.  These steps don't add much time
either.

Lastly, infer the OS when downloading tarball to avoid managing them in
the job spec.

This surfaces test failures more clearly on CircleCI by adding
testem-multi-reporter to report both via the default TAP reporter
as well as an xUnit reporter whose output is stored as an artefact.

Start collecting raw `go test -json` output to help with debugging odd
CI failures.

It's installed by default in macOS unlike wget

build darwin binaries in CI as a basic check.  Protects against
cross compile issues.

Signed-off-by: Yoan Blanc <yoan@dosimple.ch>