[gwp-asan] fix tests under clang coverage, and extend invariants

1. Fixes this test under clang coverage, which is run under presubmit
   for TEST_MAPPING files. When we spawn under a minijail, and the
   process exited normally (which is the case for recoverable), clang
   coverage would use atexit handlers to dump some stuff using banned
   prctl's and other syscalls. Instead of allow-listing them all which
   sounds like a huge pain, call _exit() which skips those handlers.

2. Extends the invariant testing to make sure that recoverable GWP-ASan
   recovers both the first time, and a second time in a different slot.

Bug: N/A
Test: CLANG_COVERAGE=true NATIVE_COVERAGE_PATHS="*" atest debuggerd_test
Change-Id: I6059e21db4c2898b1c9777a00d2a54497d80ef79