Improvements needed for DT-OTIC and NCTU deploys

- Add text/debug boot mode
- Add ability to specify network interfaces manually during install
- Documentation fixes
- Run 'apt update' in prepare, to help pass CI

Change-Id: Ie341d003b499ef2d22f2d58c38eb41016df93d5a
diff --git a/templates/ubuntu1804_preseed.cfg.j2 b/templates/ubuntu1804_preseed.cfg.j2
index 3212a14..759a0df 100644
--- a/templates/ubuntu1804_preseed.cfg.j2
+++ b/templates/ubuntu1804_preseed.cfg.j2
@@ -23,7 +23,11 @@
 d-i clock-setup/ntp-server string ntp.ubuntu.com
 
 # network and hostname
+{% if 'iface' in item %}
+d-i netcfg/choose_interface select {{ item['iface'] }}
+{% else %}
 d-i netcfg/choose_interface select auto
+{% endif %}
 d-i netcfg/hostname string {{ item['hostname'] }}
 d-i netcfg/get_domain string {{ item['domain'] }}
 d-i hw-detect/load_firmware boolean true