LU-425 tests: fix the issue of using "grep -w"

LU-425 tests: fix the issue of using "grep -w"

This patch fixes the following issue while using "grep -w"
to do exact match:

$ echo /mnt/nbp0-2 | grep -w /mnt/nbp0
/mnt/nbp0-2

Per the description of "-w" option:
-w, --word-regexp
Select only those lines containing matches that form whole words.
The test is that the matching substring must either be at the
beginning of the line, or preceded by a non-word constituent
character. Similarly, it must be either at the end of the line
or followed by a non-word constituent character. Word-constituent
characters are letters, digits, and the underscore.

So, the hyphen "-" character is a non-word constituent character
and "grep -w" does not do exact match on strings which contain it.

Signed-off-by: Yu Jian <yujian@whamcloud.com>
Change-Id: I91962910033f561cc9c9a82bd88bbb6dff5594af
Reviewed-on: http://review.whamcloud.com/2528
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-by: Wei Liu <sarah@whamcloud.com>
Reviewed-by: Johann Lombardi <johann@whamcloud.com>