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*

logd/tests/logd_test.cpp

@@ -952,7 +952,7 @@ static inline uint32_t get4LE(const char* src) {
 void __android_log_btwrite_multiple__helper(int count) {
 #ifdef __ANDROID__
     log_time ts(CLOCK_MONOTONIC);
-
+    usleep(100);
     log_time ts1(CLOCK_MONOTONIC);
 
     // We fork to create a unique pid for the submitted log messages