Add stack trace coverage to MTE tests.

It's impractical to test the contents of the stack trace, but we
should at least test that *a* stack trace is present, which would
have caught the bug fixed by r.android.com/1306754 .

Bug: 135772972
Change-Id: Ic5e0b997caa53c7eeec4e5185df5c043c9d4fe3d