LU-3971 hsm: Copytool code cleanup

Minor refactoring of the bandwidth controling code.
Deletion of a superfluous select() call on regular files.

Signed-off-by: Henri Doreau <henri.doreau@cea.fr>
Change-Id: Iae550bb69c1524865b38a92d9b7674fce2f58258
Reviewed-on: http://review.whamcloud.com/7583
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: jacques-Charles Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Reviewed-by: Faccini Bruno <bruno.faccini@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>