change at_cmd to static library

Change-Id: I9e08355738d4dcfa21ef6a75beb647f32f17e6ce
delete UI

Change-Id: I797b09a4b42161750c40b8f9e3345a573e45267c
use testkey certificate

Change-Id: I36c9080adbcc6c698707da4c1dc4d821d7acc193