show a nicer error message if the client is not authenticated

[jstrachan]

the following is a little cryptic:

Caused by: com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'Unauthorized': was expecting ('true', 'false' or 'null')
 at [Source: io.fabric8.kubernetes.client.internal.org.jboss.netty.buffer.ChannelBufferInputStream@73a19967; line: 1, column: 14]
    at com.fasterxml.jackson.core.JsonParser._constructError(JsonParser.java:1581)
    at com.fasterxml.jackson.core.base.ParserMinimalBase._reportError(ParserMinimalBase.java:533)
    at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._reportInvalidToken(UTF8StreamJsonParser.java:3448)
    at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._handleUnexpectedValue(UTF8StreamJsonParser.java:2607)
    at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._nextTokenNotInObject(UTF8StreamJsonParser.java:841)
    at com.fasterxml.jackson.core.json.UTF8StreamJsonParser.nextToken(UTF8StreamJsonParser.java:737)
    at com.fasterxml.jackson.databind.ObjectReader._initForReading(ObjectReader.java:378)
    at com.fasterxml.jackson.databind.ObjectReader._bindAndClose(ObjectReader.java:1494)
    at com.fasterxml.jackson.databind.ObjectReader.readValue(ObjectReader.java:1102)
    at io.fabric8.kubernetes.client.dsl.internal.BaseOperation.handleResponse(BaseOperation.java:433)
    at io.fabric8.kubernetes.client.dsl.internal.BaseOperation.handleGet(BaseOperation.java:463)
    at io.fabric8.kubernetes.client.dsl.internal.BaseOperation.get(BaseOperation.java:100)

wonder if we can give the user a hint they need to login via oc login or kubectl login?