LU-7086 tests: resolve /sbin symlink in test-framework.sh

LU-7086 tests: resolve /sbin symlink in test-framework.sh

In rhel7 and other new distros, /sbin is linked to /usr/sbin, so
the mount check in load_modules_local() is not matched anymore.
To avoid multiple bind mounts, this patch checks /sbin symlink
before using it directly.

Signed-off-by: Emoly Liu <emoly.liu@intel.com>
Change-Id: I287ccd81ae4187a381a7f94dee30338d20dd6155
Reviewed-on: http://review.whamcloud.com/16606
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>