Internals: Switch to v2 go.mod, drop GOPATH, and fix Azure Pipelines (#595)

* Switched to v2 go.mod

Also set GO111MODULE=on in build stuff to always use Go modules
even when in GOPATH.

* Ensure go.mod, go.sum, and vendor are up to date

* Attempt to fix Azure pipelines

* Add set -e to properly fail on exit (it didn't seem to be
  propagating properly before).
* Set workingDirectory for GoFmt and GoGen (this might be why it
  fails unlike compile and unitests).

* Another attempt to fix Azure Pipelines

* Use the Go env template for all go-related jobs.

* Completely fixed Azure Pipelines

* Added a display name to GoFmt for consistency.
* Fixed diffs for GoFmt and GoGen.
* Show git status for checks.

* Drop GOPATH for tests

TODO: Do the same for integration tests.

* Drop GOPATH for integration tests

* Show more diffs

* Regenerate provider support matrix

This wasn't done in #590...

build/azure-pipelines/integration.yml

@@ -1,9 +1,5 @@
 variables:
-  GOBIN:  '$(GOPATH)/bin' # Go binaries path
-  GOROOT: '/usr/local/go1.13' # Go installation path
-  GOPATH: '$(system.defaultWorkingDirectory)/gopath' # Go workspace path
-  modulePath: '$(GOPATH)/src/github.com/$(build.repository.name)' # Path to the module's code
-  wd: '$(modulePath)/integrationTest'
+  wd: '$(System.DefaultWorkingDirectory)/integrationTest'
 
 trigger:
   batch: "true"