Add more ptrace process resumption tests.

Add tests to verify that ptrace unlink happens immediately for unreaped
processes.

Test: /data/nativetest/bionic-unit-tests/bionic-unit-tests --gtest_filter="Ptrace*"
Test: /data/nativetest64/bionic-unit-tests/bionic-unit-tests --gtest_filter="Ptrace*"
Change-Id: I9803ee5be2a0686c21556598ecf17348df09f601