Merge branch 'ab/test-leak-diag'

Random test-framework clean-up.

* ab/test-leak-diag:
  test-lib: add "fast_unwind_on_malloc=0" to LSAN_OPTIONS
  test-lib: make $GIT_BUILD_DIR an absolute path
  test-lib: correct and assert TEST_DIRECTORY overriding
  test-lib: add GIT_SAN_OPTIONS, inherit [AL]SAN_OPTIONS