Add USan+ASan and UBSan+TSan tests to shadow-memory lit parallelism group.

Summary:
Previously we were running these tests without the "shadow-memory"
lit parallelism group even though we run the ASan and TSan tests in
this group to avoid problems with many processes using shadow memory
in parallel.

On my local machine the UBSan+TSan tests would previously timeout
if I set a 30 second per test limit. With this change I no longer
see individual test timeouts.

This change was made in response to the greendragon build bot reporting
individual test timeouts for these tests. Given that the UBSan+ASan and
UBSan+TSan tests did not have a parallelism group previously it's likely
that some other change has caused the performance degradation. However
I haven't been able to track down the cause so until we do, this change
seems reasonable and is in line with what we already do with ASan and
TSan tests.

rdar://problem/51754620

Reviewers: yln, kubamracek, vsk, samsonov

Subscribers: #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D63797

llvm-svn: 364366