Should support ADB_SERVER_SOCKET

We use adb servers on remote machines, and our tests on our CI, so we need this to support ADB_SERVER_SOCKET just like adb, without killing the remote server in case someone else is using one of the remote devices.

Version 0.10.1

Steps
1. remote.machine> adb -a -P 9125 nodaemon server
2. local> ADB_SERVER_SOCKET=tcp:remote.machine:9125 adb devices
2a. emulator-5554 device
3. local> ADB_SERVER_SOCKET=tcp:remote.machine:9125 java -jar bundletool.jar get-device-spec --output x.json
3a. No connected devices found.

**Expected behavior**

It would honour ADB_SERVER_SOCKET just like adb does - without killing the remote server.

4.15.0-51-generic #55-Ubuntu SMP Wed May 15 14:27:21 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux