xrootd-multiuser logs too frequently

[timtheisen]

During testing of xrootd-multiuser. Bockjoo Kim noted the following:

Line 179 of https://github.com/bbockelm/xrootd-multiuser/blob/master/src/multiuser.cpp#L179

prints the message too frequently in the log file.

So, that line might be commented out or printed out only with the verbose condition.