Add API acceptance tests for /archiver endpoint

[phil-davis]

PR cs3org/reva#2066 added a /download_archive API endpoint.

PR #2509 exposes the endpoint in oCIS.

Add some acceptance tests that check the endpoint works.

This is an oCIS-reva feature. The test scenarios can be added as a new test suite directly in this oCIS repo. Then we can probably move copy them into cs3org/reva as well.

[individual-it]

Now also the resources ID are supported in order to specify the content of the archive to download. see cs3org/reva#2100

[individual-it]

WIP: #2717

[individual-it]

the endpoint name in ocis is /archiver not /download_archiver

[individual-it]

Some tests have been added (see PRs in the list above)
I'm closing this issue now, feel free to reopen if more tests are required. Ideas for more tests would be

• invalid data
• mixed path & ids potential issue: Add support for resource id to the archiver cs3org/reva#2100 (comment)
• different permissions on received shares
• etc

CC @micbar @ScharfViktor