GELF appender: move facility key into a custom field if present

At the same time, don't assign a default value as the field is optional
according to the GELF spec v1.1.
GELF appender: set version to 1.1
fix gelfAppender-test.js to reflect the above changes
reflect the above changes ; forgot a facility field
fix uninitialized field error
fixed up test after merge
Merge 2ion-gelf-spec-v1.1-compliance into master