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.