LU-10070 utils: SEL: lfs find & getstripe support

LU-10070 utils: SEL: lfs find & getstripe support

The support includes:
- add --extension-size option to lfs find & getstripe along
  with +/- functionality;
- do not take the extension components into account for
  lfs find --stripe-size and --stripe-count;
- add appropriate tests;

Cray-bug-id: LUS-2528
Signed-off-by: Vitaly Fertman <c17818@cray.com>
Change-Id: Ic3ad4c713e8c676998cf7d02b524ba266c992924
Reviewed-on: https://review.whamcloud.com/34909
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexey Lyashkov <c17817@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>