resolver list is not cleared on rebuild

Refactoring ResolverActivity.java

Change-Id: I84e6420ff98ddcafd27a52b041ddb1c50e7d7362
Signed-off-by: You Kim <you.kim72@gmail.com>
Re-use existing thread

Bug: 7377541
Change-Id: I097f2288ebfc2b4a9782cbced19d9c36d0703acb