[v6r11] XRootStorage: putFile would place file in the wrong location on eos

This PR cherry picked a fix from @chaen for v6r12, but adds an important fix.
(https://github.com/DIRACGrid/DIRAC/commit/3039730f1921d3ef381f9e588a1721e70fa3c762)

putFile calls would place files in 
/eos/clicdp/grid/eos/clicdp/grid/ilc/user/s/sailer/
instead of 
/eos/clicdp/grid/ilc/user/s/sailer/
before.

Things seem to be working, but now three slashes instead of two are present in the URL...
e.g: root://eospublic.cern.ch///eos/clicdp/grid/ilc/user/s/sailer/test4.stdhep