wafsamba: pass environment to cross-execute tests

wafsamba: pass environment to cross-execute tests

This can come in handy for cross-execute scripts in general, and
is particularly required by the samba-xc test for cross-answers /
cross-execute, because Samba sets LD_LIBRARY_PATH during rpath
checks, and the test program needs that in order to successfully
run.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13846

Signed-off-by: Uri Simchoni <uri@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>