Fixes issue #517: Determines Kubernetes version using the REST API (#518)

* Fixes issue #517: Determines Kubernetes version using the REST API

* fixes

* fixes

* adds tests

* fixes

* added more tests

* kubernetes_version_test: Add a missing case for invalid certs

Signed-off-by: Simarpreet Singh <simar@linux.com>

* kubernetes_version_test: Remove un-needed casts

Signed-off-by: Simarpreet Singh <simar@linux.com>

* fixes as per PR review

* fixes as per PR review