Change pull policy for helper pod to IfNotPresent

https://github.com/rancher/local-path-provisioner/issues/22

Thanks to @km4crus , we've added ARM64 support.

MAY help https://github.com/rancher/local-path-provisioner/issues/14

Thanks to @vvitkovskiy, now the helper pod tolerates all the taints.

Since the pod is able to use the node, the helper pod should be able to
run on the node as well.

Use alpine based image for smaller image size.

1. Update Dockerfile.dapper to install Go 1.12, separate go gets for better image layer caching

2. replace ubuntu image with simple alpine base image

3. add linker flag -w for smaller binary

4. gitignore some generated files

Fix the deployment in non-default namespace

When deploying this provisioner in non-default namespace, this provisioning fails with an message about missing local-path-storage. 

As per the deployment file, Namespace is passed using the string POD_NAMESPACE.  (https://github.com/rancher/local-path-provisioner/blob/master/deploy/local-path-storage.yaml#L75)

This PR is to correct the variable name used for fetching the namespace.

Thanks to Reinhard Nägele <unguiculus@gmail.com>, one additional PR has
been merged to correctly fix https://github.com/rancher/local-path-provisioner/issues/7 .

See commit message and https://github.com/rancher/local-path-provisioner/pull/9 for details

This is a follow-up PR for #7, since https://github.com/rancher/local-path-provisioner/commit/3256bdf61b14c6b7e517ede0f56cfebeaf28e616, unfortunately, did not fully fix the issue.

The example I supplied is not ideal. It works with your fix because it uses Busybox which doesn't have group 1000 so the user runs with gid=0. I added `id` to the script which prints the following:

`uid=1000 gid=0(root) groups=0(root),1000`

Now, when I use an image that actually has a user with uid=1000, gid=1000, such as `jenkins/jenkins` it doesn't work because the user does not belong to group 0 in this case:

`uid=1000 gid=0(root) groups=0(root),1000`

This fixes the issue using `0777` as Minikube does.

Added security context support and helper image parameter

For all the examples, create pvc using `pvc.yaml` first.

The permission of directory is 0770, because when a user login as group
e.g. group 1000, they're also belong to group 0. The default permission
for host path is 0700, which prevent group 0 from accessing the directory.

Fixes https://github.com/rancher/local-path-provisioner/issues/7 .

Also added test case `security-context.yaml` derived from @unguiculus 's
comment on the issue.

Remove Troubleshooting section for v1.11.

Also remove support for Kubernetes v1.11.

Fix provisioner to work with v1.12

Add uninstall

Refresh every 5 seconds by default

In order to setup default config.