Avoid get same timestamps in log testcase

for arm64, userspace get time by vDSO, no syscall overhead.
multiple_test_2 sometimes get 2 same timestamps now, then testcase
fails.

Bug: b/135555666
Test: ./CtsLogdTestCases64 --gtest_filter=*multiple_test*
Merged-In: Ic8a0ab6f571df1487fe5fb4e5f07dc612af69001
Change-Id: I83f8beae168f397a347972c5e60de86d16c8f7c6