Extend test suite to cover expired locks

[glpatcern]

The idea here is to create a short-living lock and get it back / refresh it after it expired, to exercise this part of the logic.

Should be pretty easy with local storage, though the code as of now does NOT validate the expiration time. The real interest though is to run this test against Reva, once #57 is completed.

[glpatcern]

With more thoughts, for the time being the Lock API shall return expired locks and shall not infer anything, so in terms of test suite nothing would change. The WOPI server business logic handles expiration internally.