LU-6219 utils: remove O_NONBLOCK usage for archive file

LU-6219 utils: remove O_NONBLOCK usage for archive file

In the first implementations of Posix copytool, file archive/restore
was using a loop around select() with handling/retry on EAGAIN.
This was later found as useless for regular files and fixed/changed
in patch for LU-3971 (http://review.whamcloud.com/7583, commit
397ebc93cef378e6d77450cdd095e2737b94f2f6).
But the O_NONBLOCK flag usage, during open() of file on archive, has
been kept since and must be removed, even if ineffective, to improve
code clarity.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: Ie6350e6f3951545f50783c9fff6753793b7a9a33
Reviewed-on: http://review.whamcloud.com/13672
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Robert Read <robert.read@intel.com>
Reviewed-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>