Git commits in Moodle 3.4.4 by David Balch

commit 2d8ba1ea5e50f56b094685a48a4be1c6ea09142b
Author: David Balch <david.balch@conted.ox.ac.uk>
Date:   Mon, 28 May 2018 12:42:16 +0800
Tag:    v3.4.4

MDL-57742 core_lib: Make tool_consumer_instance_guid optional