Create 2-node kind cluster since topology support is added to hostpath

Signed-off-by: Mucahit Kurt <mucahitkurt@gmail.com>

prow.sh: install dep if needed

"make test-vendor" depends on dep if the current project uses
dep. Without it, the vendor directory checking was skipped under Prow.

Add rule for building Windows binaries

Signed-off-by: Deep Debroy <ddebroy@docker.com>

Update kind to v0.5.0

Fix CI jobs on Kubernetes master

changes to kind. There are 3 changes made to prow.sh:

1. Use a master commit of kind that includes the fix for Kubernetes
master.
2. Use git clone instead of git checkout (shallow) to source Kubernetes.
This lets kind correctly figure out the Kubernetes release tag.
3. Build kind with make install. The kind fix was not working correctly
when built with go build.

prow.sh: tag master images with a large version number

Add 1.15 jobs

with specific patch versions that kind 0.4.0 supports. Also, feature
gate setting is only supported on 1.15+ due to
kind.sigs.k8s.io/v1alpha3 and kubeadm.k8s.io/v1beta2 dependencies.

more flexible test driver config

By moving the code into a separate function, other CSI drivers have a
chance to overwrite it. For the hostpath driver itself we need the
ability to set the driver name depending on which revision is getting
installed.

build.make: allow repos to use 'go mod' for vendoring

How a repo does vendoring is detected based on the presence of
Gopkg.toml.

The vendor check with `dep` was all done locally, but the
corresponding check for `go mod` requires network access. The check
therefore gets skipped when running in the Prow CI in situations where
we are sure that it isn't needed (for example, in a periodic job).

update to Go 1.12.4

Kubernetes also requires 1.12. We pick the latest stable release
for CI builds.

prow.sh: skip sanity testing if component doesn't support it

Whether a component supports sanity testing depends on the
component. For example, csi-driver-host-path enables it because it
makes sense there (and only there). Letting the prow.sh script decide
whether it actually runs simplifies the job definitions in test-infra.

prow.sh: update csi-driver-host-path

This pulls in
https://github.com/kubernetes-csi/csi-driver-host-path/pull/37, which
turned out to be necessary for pre-submit testing of the
livenessprobe.

build.make: Replace 'return' to 'exit' to fix shellcheck error

prow.sh: remove AllAlpha=all, part II

This was already meant to be done earlier in cda2fc58.
While at it, extend the permanent TODO with guidance on future feature
gates.

prow enhancements

It turned out to not work. Instead of reverting the commit which
introduced this, let's better document this explicitly.

When KinD fails in a Prow job, we need additional information to
understand why it failed.

Not all environments have Docker. The simplifying assumption here is
that if the Docker command is available, it's also usable.

When running only some tests, sometimes extra, unnecessarily work was
done, like bringing up the cluster without alpha gates.

The previous logic failed for canary jobs, those also deploy a recent
driver. Instead of guessing what driver gets installed based on job
parameters, check what really runs in the cluster and base the
decision on that.

We only need to maintain this blacklist for 1.0.x until we replace it
with 1.1.0, then this entire hostpath_supports_block can be removed.

"grep -w" treated "serial-alpha" as two words and therefore
CSI_PROW_TESTS sometimes ran too many tests.

This ensures that also new, currently unknown alpha gates are enabled
when testing against a future Kubernetes versions. For all currently
known Kubernetes versions we just use the minimal set of alpha gates,
which ensures that we don't miss any of them in our documentation.