Update EOS to version 5.2.x (x > 17)

When looking in #615 (closed) we found the hard way that eos 5.2.7 droped attr command and this was replaced by xrootd xattr command (in xrootd 5.6.z).

Basically the call we have in CI is a xrootd command that was calling eos attr now defunct command.

The problem was discussed in #615 (closed) and we need to target for something that can work for us in CI:

• if xrootd client version is too old (< 5.6.1) -> skip the attr tests (attr get for retrieve and eviction counter tests)
• otherwise go for xrdfs xattr command to get the attributes we need and perform the tests

This should be tested in our EOS CI mockup: we will use xrdfs xattr from now on for our attributes tests.