[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).

(cherry picked from commit 33c0cdd238dae97b63ad84fb7b9d89b716facbf0)
Signed-off-by: Libor Zoubek <lzoubek@redhat.com>