Error messages in RangerRESTClient aren't helpful

Currently, if the user accidentally configures the SSL settings incorrectly, or the keystore/truststore is not exists or not readable, then the user will receive a not too helpful 'SSLContext must not be null' coming from the com.sun.jersey.client.urlconnection.HTTPSProperties

This happens, because RangerRESTClient.getKeyManagers / getTrustManagers / getSSLContext methods are catching the exceptions, and are returning null, instead of failing fast, so the user could easily act and fix the issues