composer: 2.4: fix VTS usage of desired time

Test_setActiveConfigWithConstraints is setting the desired time
for a config change to be before the test starts.
This causes the test to use the same value for all configurations,
which becomes stale the more configurations the device supports.
This fix is setting the desired time before calling
to setActiveConfigWithConstraints.

Bug: 161023185
Test: adb shell data/nativetest64/VtsHalGraphicsComposerV2_4TargetTest/VtsHalGraphicsComposerV2_4TargetTest
Change-Id: I236e5c9c16b4ba730677cd4c980a7071ba25840e