LU-4665 tests: support specifying arbitrary OST indices

LU-4665 tests: support specifying arbitrary OST indices

This patch improves Lustre test framework to support specifying
arbitrary OST indices via OST_INDEX_LIST or OSTINDEX${num}.

For example,

OSTINDEX1="1"
OSTINDEX2="2"
OSTINDEX3="4"
......
or
OST_INDEX_LIST="[1,2,4-6,8]" #[n-m,l-k,...], where n < m and l < k

The default index of an individual OST is its facet number minus 1.

Function facet_index() is added to get index for a facet.

Test-Parameters: alwaysuploadlogs \
envdefinitions=OST_INDEX_LIST=[0-5] ostcount=7 \
testlist=sanity,conf-sanity

Signed-off-by: Jian Yu <jian.yu@intel.com>
Change-Id: Icf5d377d4d10995c2fb501bf7762ec8937466fdc
Reviewed-on: http://review.whamcloud.com/9722
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>