Python interface does not expose the Prepare::Evict flag

[esindril]

The prepare evict flag used for tape backends (e.g CTA) is not exposed in the Python interface:
https://github.com/xrootd/xrootd/blob/master/bindings/python/libs/client/flags.py#L87
This is defined in the C++ part here:
https://github.com/xrootd/xrootd/blob/master/src/XrdCl/XrdClFileSystem.hh#L185

Note that the value of kXR_evict is 0x0100000000 which can not be stored in a b (int) [unsigned char] when doing the parsin from the python bindings:
https://github.com/xrootd/xrootd/blob/master/bindings/python/src/PyXRootDFileSystem.cc#L618

So besides it not being defined in the enum, I could not pass it manually from the Python bindings since this then throws and OverflowError exception.