s3/util: mvxattr, a tool to rename extended attributes

s3/util: mvxattr, a tool to rename extended attributes

Usage: mvxattr -s STRING -d STRING PATH [PATH ...]
  -s, --from=STRING         xattr source name
  -d, --to=STRING           xattr destination name
  -l, --follow-symlinks     follow symlinks, the default is to ignore them
  -p, --print               print files where the xattr got renamed
  -v, --verbose             print files as they are checked
  -f, --force               force overwriting of destination xattr

Help options:
  -?, --help            Show this help message
  --usage               Display brief usage message

Bug: https://bugzilla.samba.org/show_bug.cgi?id=12490

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Fri Feb 10 22:24:59 CET 2017 on sn-devel-144