After commit Ieb03aaba887492819f9c58aa67f7acfcea81720e, the command
location-update is totally broken now. This patch removes the updating
for an image from non-empty to empty since it's not supported now.
And also removing the default value of metadata for location-update
cli command because now the only purpose of location-update is updating
the location's metadata, so it doesn't make sense to give it a default
value which may update existing metadata by mistake.
Closes-Bug: #1537626
Change-Id: I9ce98e6c63996bbfdbc56761055e37a871f9d3e2
8b6dbb2065