EZP-23441: More legacy uri handling

XML parsing from imageStorage has been moved to the LegacyStorage image gateway,
and the legacy url redecorator injected to this service.

No manual stripping/adding / to uris manually.
EZP-23441: Tweaked IO setup of legacy tests

1. Made sure that vardir cleanup and data init are in sync

2. Reordered tests in BaseIntegrationTest: the test update with no change
was done between testUpdate and its data test methods. This was resetting
the repository. It doesn't matter for most tests, but it does for image test:
when testing the updated data, we need the vardir to be untouched after
update.
Merge pull request #1039 from ezsystems/EZP-23441-io_url_decoration

EZP-23441: IO url decoration