fix(topokey): changing topology key to unique name

There are setups where nodename is different than the hostname.
The driver uses the nodename and tries to set the "kubernetes.io/hostname"
node label to the nodename. Which will fail if nodename is not same as
hostname. Here, changing the key to unique name so that the driver can set
that key as node label and also it can not modify/touch the existing node labels.

Now onwards, the driver will use "openebs.io/nodename" key to set the PV node affinity.
Old volumes will have "kubernetes.io/hostname" affinity, and they will also work as
after the PR https://github.com/openebs/zfs-localpv/pull/94, it supports all the node
labels as topology key and all the nodes have "kubernetes.io/hostname" label set. So
old volumes will work without any issue. Also for the same reason old stoarge classes
which are using "kubernetes.io/hostname" as topology key, will work as that key is supported.

This fixes the issue where the driver was trying to create the PV on the master node
as master node is having "kubernetes.io/hostname" label, so it is also becoming a valid
candidate for provisioning the PV. After changing the key to unique name, since the driver
will not run on master node, so it will not set "openebs.io/nodename" label to this node
hence this node will never become a valid candidate for the provisioning the volume.

Signed-off-by: Pawan <pawan@mayadata.io>

unreleased/101-pawanpraka1

@@ -0,0 +1 @@
+ changing topology key to unique name to avoid collision with the existing node label