Fixed JERSEY-1800.

- Passing empty string to UriBuilder.uri(String) method does not fail anymore. As per URI RFC-3986, empty string is a valid path (or scheme-specific part). So the new behaviour replaces UriBuilder & UriParser behaviour treats an empty string as a relative, empty path (empty scheme specific part) URI reference.

Change-Id: Iad15b428a990fff5b3de8f353ab4c5d9b45bd877
Signed-off-by: Marek Potociar <marek.potociar@oracle.com>