Make minimum gc sleep time tunnable Bug: 241601436 Test: check smart idle maint log of StorageManagerService Signed-off-by: Daeho Jeong <daehojeong@google.com> Change-Id: I004bb6752e84d26b041cfdd27848949f6e49d05e Merged-In: I004bb6752e84d26b041cfdd27848949f6e49d05e