adb: fix exit of "adb root" when it is a no-op.

"adb root" creates a socket, then starts the service.
Socket creation should not set the exit_on_close when the service will be
a no-op.

Bug: 6259353
Change-Id: Ie526d2fad64f39a48051ed0ff6fb3405c2802ced
1 file changed