LU-16503 utils: add --hex-idx option for lfs getstripe

LU-16503 utils: add --hex-idx option for lfs getstripe

The --hex-idx option for lfs getstripe and getdirstripe makes
them output OST and MDT indexes in hex.

In addition, this commit modifies the YAML parser to treat input
like "0x[0-9a-f]+" as a number so that lfs setstripe --yaml can
accept output produced by lfs getstripe --yaml --hex-idx.

Signed-off-by: Thomas Bertschinger <bertschinger@lanl.gov>
Change-Id: I98eaa9741db787bcf4516648e58e92c7520d8640
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50340
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Olaf Faaland <faaland1@llnl.gov>
Reviewed-by: Oleg Drokin <green@whamcloud.com>