functional-tests: Consolidate and clean up 600-applications-camera

Two of the four tests still fail right now, due to the filesystem miner
not removing the metadata for photo resources when they are deleted on disk.
functional-tests: Hack 600-applications-camera into working on my machine

Seems that fs miner sometimes ignores deletes if they come quickly after
creations. But, this only seems to be for photos, and not videos. Further,
if the time.sleep(2) call is added to the videos tests, they *stop* working
due to the delete not really taking effect. Things are very broken in this
area, it seems.
functional-tests: Avoid another miner_fs_wait_for_idle
Always guarantee metadata

The --enable-guarantee-metadata flag is required for the functional tests to
pass. I don't understand why this behaviour is conditional in the first place.
Let make it always enabled and remove the flag.

When merged, jhbuild should be updated to remove the flag too!
functional-tests: Allow waiting for a certain property to be set

Just waiting for resource creation is not enough. Sometimes the test requires
that tracker-extract has processed the resource too. We can wait for that by
watching for the insertion of a triple that we know is set by tracker-extract.

This is necessary for the writeback tests to work.