avila xenial+systemd port takes too long to boot to GUI

[You-Sheng Yang]

We found devices will take about 80 seconds to show the ubuntu flash UI, and after about 60 seconds to show the login UI.
So it will take more than 2 minutes to boot up the system.

[[1. on xenial+systemd/arm64]]:
Second boot time:
Without flight mode: 25s to ubuntu splash, 93s to login dialog
With flight mode: 46s to ubuntu splash, 120s to login dialog
Without flight mode, but disable ofono completely: 84s to ubuntu splash, 143s to login dialog. Worse cases are also observed.

$ adb shell system-image-cli -i
current build number: 84
device name: frieza_arm64
channel: ubuntu-touch/staging/ubuntu
last update: 2016-11-17 03:23:16
version version: 84
version ubuntu: 20161117
version device: 20161014.0
version custom: 20161117

[[2. on vivid+upstart/armhf]]:
Second boot time:
Without flight mode: The worse case I got is 78s to ubuntu splash, 92s to login dialog. However I have this only once and am never able to reproduce the same. The usual cases have almost no difference from the following two cases. All boot to splash in 10s and login dialog in around 22s.

With flight mode: 9s to ubuntu splash, 19s to login dialog
Without flight mode, but disable ofono completely: 9s to ubuntu splash, 21s to login dialog

$ adb shell system-image-cli -i
current build number: 235
device name: frieza
channel: ubuntu-touch/rc-proposed/bq-aquaris-pd.en
last update: 2016-11-19 11:56:02
version version: 235
version ubuntu: 20161119
version device: 20160809.0
version custom: 20160831--42-26-vivid

[[Debug Tips]]

1. Flash xenial user build:

  $ ubuntu-device-flash touch --bootstrap --wipe \
    --channel=ubuntu-touch/staging/ubuntu \
    --device=frieza_arm64 [--recovery-image=recovery.img]

2. Flash vivid user build:

  $ ubuntu-device-flash touch --bootstrap --wipe \
    --channel=ubuntu-touch/rc-proposed/bq-aquaris-pd.en \
    --device=frieza [--recovery-image=recovery.img]