[BZ 1075875] remote API client version is 'undefined' when client is
packaged as executable JAR

if rhq-client.version-check=false - do not even try to detect the version
and log any message - this is exactly what this property says : "NO version
check, please"

introduced 'rhq.client.version' system property, that you can set or pass to
your client that would take precedence over what could be found in manifest
(if it exists).