Add @volatile to MIME-Types tests

[Gomez]

The MIME-Types test in the current tests are volatile on different Installations (PHP version, unix version ...)
We could factor the tests out and add a @volatile tag.

A cucumber.yml file could help us add defaults runs without the @volatile:

https://github.com/cucumber/cucumber/wiki/cucumber.yml

[PVince81]

Note that in OC6 the mime types aren't based on file contents any more due to performance.
There is now a mapping between file extension and mime type (I don't know where in the OC code yet).
That might simplify the tests a bit ?

[PVince81]

Ok got it, it's here: https://github.com/owncloud/core/blob/master/lib/private/mimetypes.list.php