Fix nobuild runs of run_net_test.sh without KERNEL_BINARY env var set

This commit sets the default location of KERNEL_BINARY based on the
architechture, and ensures that it is set for --nobuild runs as well.

Test: Ran kernel unit tests
Change-Id: I0db4f3aaab811cc0aec0406f24e4a2506cbe694a
1 file changed
tree: 836f691af16a7d8e4aaefc8e3370af8b30f26faf
  1. devicetree/
  2. net/
  3. Android.bp