When NewK8sClient() detects and error, it used to call FatalLogMsg()
which causes a panic. There are additional features that can be used on
Kubernetes clusters, but these are not a requirement for most
functionalities of the driver.
Instead of causing a panic, returning an error should suffice. This
allows using the driver on non-Kubernetes clusters again.
Fixes: #2452
Signed-off-by: Niels de Vos <ndevos@redhat.com>