Changing for new dl directory structure.
Changes to functional tests for new dl directory structure.
No need to test for arch validation

We no longer need to validate the architecture as the download
is no longer arch-specific, so fix the tests which check that
arch validation is working correctly.
We no longer need ARCHS, as we don't validate

The VersionsFetcher no longer fetches a download list for
a specified architecture, so we don't need an ARCHS constant
which enumerates the valid architectures.
[ArchiveFetcher] Add a catch-all for errors

In the download/unpack chain, we might get errors occurring at
unpack time. Add a handler to the done() call which catches
any errors coming from the Unpacker instance.
Remove redundant test
Fix ArchiveFetcher progress test

* Logger only gets called 3 times, not 4 (as we removed a step)
* The output directory doesn't have xwalk_app_template in it any
  more, as we've removed an unpack step, so the expected directory
  path is different.
Merge pull request #57 from crosswalk-project/maxw-new-dl-dir-structure-rebase

changes for new dl dir structure