Regression tests portability: Do not 'cd' into volume

Changing current directory to the root of the volume to
execute tests from there keeps an open file descriptor
to it that could interfere with some tests.

I've removed all 'cd' and used abosulte paths on all
tests.

Change-Id: Ic54afb7d7974e9e80818201bcd99ee2b01d00442
BUG: 1129939
Signed-off-by: Xavier Hernandez <xhernandez@datalab.es>
Reviewed-on: http://review.gluster.org/9151
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Emmanuel Dreyfus <manu@netbsd.org>
Tested-by: Emmanuel Dreyfus <manu@netbsd.org>