Refactor error handling for K8sError and BuildClientError
remove unused error classes and handle all "HTTPError"s the same way since they all have the same signature. This allows us to catch unknown errors such as the one described in https://phabricator.wikimedia.org/T337903
Bug: T337903 Signed-off-by: Ndibe Raymond Olisaemeka NdibeRaymond1@gmail.com