[Sanitizers] Set default allocator_release_to_os_interval_ms to 5 seconds

Summary:
With new release to OS approach (see D38245) it's reasonable to enable
it by default. Setting allocator_release_to_os_interval_ms to 5000 seems
to be a reasonable default (might be tuned later, based on the
feedback).

Also delaying the first release to OS in each bucket for at least
allocator_release_to_os_interval_ms after the first allocation to
prevent just allocated memory to be madvised back to OS and let short
lived processes to avoid release to OS overhead altogether.

Reviewers: cryptoad

Subscribers: kubamracek, llvm-commits, mehdi_amini

Differential Revision: https://reviews.llvm.org/D39318

llvm-svn: 316683