clean data as install

[Yuan-Chen Cheng]

the --bootstrap command will clean all existing data inside /data.

For dual boot, we need only delete file / directory that ubuntu touch use.

The following are file that ubuntu touch use (get on a flash install n4
with Trusty, devel channel, rev 58, version ubuntu: 20131211, version device: 20131203)
-------------------
-rw-r--r-- 1 root root 3 Dec 13 06:01 .last_ubuntu-build
-rw-rw-rw- 1 root root 0 Dec 13 06:00 .last_update
-rw------- 1 root root 2 Dec 6 01:56 .layout_version
-rw------- 1 root root 536870912 Dec 13 06:00 SWAP.img
drwxrwx--x 24 system system 4096 Dec 13 06:02 android-data
drwxr-xr-x 2 root root 4096 Dec 13 06:06 media
drwxr-xr-x 6 root root 4096 Dec 13 06:01 system-data
-rw------- 1 root root 2097152000 Dec 13 06:00 system.img
drwxr-xr-x 3 root root 4096 Dec 13 05:56 user-data

[Yuan-Chen Cheng (ycheng-twn)]

it seems that media directory is also used by android. so I'll not remove media directory.

[Yuan-Chen Cheng (ycheng-twn)]

.last_ubuntu-build => keep
.last_update => keep
.layout_version => remove as format system
SWAP.img => remove as format data
android-data => backup of android data. I can't find the code that is doing this backup from android_bootable_recovery (git://phablet.ubuntu.com/CyanogenMod/android_bootable_recovery)
media: shared with Android, keep
system-data: ubuntu directories (etc, lib, opt, var) remove as format data
system.img: remove as format system (existing code)
user-data: mapping to /home in ubuntu, remove as format data

[Ethan Chang (ethan.chang)]

Verified in ubuntuinstaller build 68.