Fix EVS VTS test cases

This change modifies logics to verify test results that need to parse
events from EVS manager.  Especially, test cases that run multiple
camera clients spawn threads to listen EVS events.

Also, this updates waitForEvent() method to return more precise results.

Bug: 142275664
Test: VtsHalEvsV1_1Target
Change-Id: Ic328217be1e49a3a862facf783a5356ac34ce9ed
Signed-off-by: Changyeon Jo <changyeon@google.com>