adding auth client isEnabled check before loading the properties file fo...

...r authentication client configuration

based of , https://github.com/caskdata/cdap-ingest/pull/72, opening against release/1.0.0 as per @poornachandra suggestion.
Also, a1.sinks.sink1.verifySSLCert should go right after line 31 documentation of a1.sinks.sink1.sslEnabled, as they are related.