Fix assembler test to use path if it can't find tools.
Fix assembler test to use path if it can't find tools.

This fixes build breakage.

Change-Id: I8074d47f1c1470cf886d517e9e68a6a6b4330485

treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst