no adb access under xenial+systemd user build

[You-Sheng Yang]

adb service under user build involves several other parties and is currently not implemented.

[You-Sheng Yang (vicamo)]

However, like what we've have for eng build, one may simply hook android-tools-adbd service to another valid property under user build, e.g. "ro.build.type=user".

device# cd /ubuntu/etc/systemd/system
device# mkdir <email address hidden>\\x3duser.target.wants
device# cd <email address hidden>\\x3duser.target.wants
device# ln -s /lib/systemd/system/android-tools-adbd.service

Here, the folder name is "android-container@<KEY>\x3d<VALUE>.target.wants". That backslash character is required.

[You-Sheng Yang (vicamo)]

After some discussion, we can also enable "ro.debuggable=1" in user builds temporarily and revert it when all is ready.

[You-Sheng Yang (vicamo)]

Temp work-arounds have been proposed. Please keep this bug open even if they're merged later.

[You-Sheng Yang (vicamo)]

All necessary changes merged.

[Yuan-Chen Cheng (ycheng-twn)]

verify the following build have adb after turned on in system-settings.

current build number: 68
device name: frieza_arm64
channel: ubuntu-touch/staging/ubuntu
last update: 2016-10-26 00:51:22
version version: 68
version ubuntu: 20161025
version device: 20161014.0
version custom: 20161025