CP-6167: The xenbuilder chroot env has no /dev/tty

It seems that the xenbuilder chroot env doesn't have /dev/tty. So in
the build log, we saw "tee: /dev/tty: No such device or address"

This is strangely different from the local chroot testing env I
created using standard xenbuilder command "make sm-chroot" when
doing test.

This quick fix avoids using the "tee /dev/tty" trick and do it in
a plain/verbose way.

Signed-off-by: Zheng Li <zheng.li@eu.citrix.com>
Reviewed-by: Vineeth Thampi Raveendran <vineeth.thampi@citrix.com>