install network-checks's dependencies

Since it runs before the real setup begins, we must make sure that packages are installed.

Also removing bind9-host's installation from system.sh. In 189dd6000e I added this so we could use `host`
to aid Docker autoconfiguration. Docker support was since removed but this hadn't gotten removed, which lead me to think it was
normally installed by Ubuntu. It's now installed in `network-checks.sh`.

fixes #180

setup/network-checks.sh

@@ -1,3 +1,7 @@
+# Install the 'host', 'sed', and and 'nc' tools. This script is run before
+# the rest of the system setup so we may not yet have things installed.
+hide_output apt-get -y install bind9-host sed netcat-openbsd
+
 # Stop if the PRIMARY_HOSTNAME is listed in the Spamhaus Domain Block List.
 # The user might have chosen a name that was previously in use by a spammer
 # and will not be able to reliably send mail. Do this after any automatic

setup/system.sh

@@ -16,7 +16,7 @@ hide_output apt-get -y upgrade
 #   	fail2ban: scans log files for repeated failed login attempts and blocks the remote IP at the firewall
 
 apt_install python3 python3-pip \
-	wget curl bind9-host \
+	wget curl \
 	haveged unattended-upgrades ntp fail2ban
 
 # Allow apt to install system updates automatically every day.