docker: Don't use a hardcoded root password

Best practice is to use unprivileged service daemons inside Docker
containers.  But with this hardcoded root password, in the case of
remote code execution, an attacker could trivially escalate their
privileges to root/uid 0.  And while that's uid 0 inside a container,
that's a much larger attack surface.

Instead, do the same thing we're doing for the Cloud images: lock the
root password, create a user to make Anaconda happy, then delete the
user in %post.

https://bugzilla.redhat.com/show_bug.cgi?id=1175997

fedora-docker-base.ks

@@ -18,7 +18,8 @@
 cmdline
 bootloader --location=none
 timezone --isUtc --nontp Etc/UTC
-rootpw --plaintext qweqwe
+rootpw --lock --iscrypted locked
+user --name=none
 
 keyboard us
 zerombr
@@ -44,6 +45,9 @@ dnf-yum  # https://fedorahosted.org/fesco/ticket/1312#comment:29
 # Set the language rpm nodocs transaction flag persistently in the
 # image yum.conf and rpm macros
 
+# remove the user anaconda forces us to make
+userdel -r none
+
 LANG="en_US"
 echo "%_install_lang $LANG" > /etc/rpm/macros.image-language-conf