Remove systemd managed dnsmasq in dockerfile

Since we are running dnsmasq container in privileged mode, running
dnsmasq as systemd service in the container causing some issue like
when VM comes up, it shows centos in boot/login screen.
 - #695 (comment)

images/dnsmasq/Dockerfile

@@ -2,12 +2,11 @@ FROM centos:8
 MAINTAINER CodeReady Container <devtools-cdk@redhat.com>
 
 RUN yum -y install dnsmasq && \
-    yum clean all && \
-    systemctl enable dnsmasq
+    yum clean all
 
 COPY dnsmasq.conf /etc/
 COPY resolv.dnsmasq.conf /etc/
 
 EXPOSE 53/udp
 
-CMD [ "/sbin/init" ]
+ENTRYPOINT ["/usr/sbin/dnsmasq", "--keep-in-foreground"]