[scudo] lower quarantine default sizes

Summary:
After discussing the current defaults with a couple of parties, the consensus
is that they are too high. 1Mb of quarantine has about a 4Mb impact on PSS, so
memory usage goes up quickly.
This is obviously configurable, but the default value should be more
"approachable", so both the global size and the thread local size are 1/4 of
what they used to be.

Reviewers: alekseyshl, kcc

Reviewed By: alekseyshl

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33321

llvm-svn: 303380