[Sanitizers] Move allocator_returns_null.cc test to common.

Summary:
Add allocator_returns_null.cc test to sanitizer_common and
remove all sanitizer-specific ones except:
- HWASan is not covered by sanitizer_common
- TSan allocator does not have comprehensive error reporting yet

Reviewers: vitalybuka

Subscribers: kubamracek, delcypher, #sanitizers, llvm-commits

Differential Revision: https://reviews.llvm.org/D47971

llvm-svn: 334433