adbd: adb root should terminate adbd only if it's debuggable

adb root command will terminate adbd when closing the socket if current
user id is not root. This works for userdebug build, as adb root causes
re-enumeration.

But for user build, adb root command won't cause re-enumeration, and if
adbd is terminated and restarted, it will be in offline state, thus it
won't send any thing to host.

Change-Id: I81216a3b3da888cd9b236060cf745175f6d93c60
Author: jzhuan5 <jin.can.zhuang@intel.com>
Signed-off-by: Bo Huang <bo.b.huang@intel.com>