Enable Windows rbe_repo tests in CI

[sunjayBhatia]

This issue is for tracking enabling rbe_repo tests in CI. Currently these are disabled as we don't have a CI environment that allows us to pull Windows Docker images. Once we do, we should enable the Windows tests in CI and potentially add some integration testing to add to Windows coverage.

In addition, we should change the container image used by the WORKSPACE rbe_autoconfig rules used for tests to one owned by the bazel-toolchains maintainers. Currently these rules use an image from the Envoy project Windows build toolchain.

These sections should be updated once we have a place to copy this container image:

bazel-toolchains/WORKSPACE

Lines 275 to 277 in 834b89b

	digest = "sha256:776f241c2693f3f2187d998dcc98d2b339dcb80c99ef59bccefad0eea6e61284",
	registry = "gcr.io",
	repository = "envoy-ci/envoy-build-windows",

bazel-toolchains/WORKSPACE

Lines 424 to 431 in 834b89b

	digest = "sha256:776f241c2693f3f2187d998dcc98d2b339dcb80c99ef59bccefad0eea6e61284",
	export_configs = True,
	registry = "gcr.io",
	repository = "envoy-ci/envoy-build-windows",
	toolchain_config_spec_name = "test_config_dir",
	toolchain_config_suite_spec = {
	"container_registry": "gcr.io",
	"container_repo": "envoy-ci/envoy-build-windows",

bazel-toolchains/tests/rbe_repo/BUILD

Line 356 in 834b89b

regexp = "sha256:776f241c2693f3f2187d998dcc98d2b339dcb80c99ef59bccefad0eea6e61284",

We can probably copy the latest image from here to a bazel-toolchains owned repo in GCR: https://hub.docker.com/r/envoyproxy/envoy-build-windows2019/tags

[sunjayBhatia]

cc @wrowe