Update Dockerfile_rocky

Signed-off-by: Shubhangi-dell <shubhangi_srivastava@dell.com>

control_plane/roles/provision_cobbler/files/Dockerfile_rocky

@@ -1,4 +1,4 @@
-FROM rockylinux/rockylinux:8.5
+FROM rockylinux/rockylinux:docker_os
 
 # RPM REPOs
 RUN dnf install -y \
@@ -66,4 +66,4 @@ VOLUME [ "/var/www/cobbler", "/var/lib/cobbler/backup", "/mnt" ]
 
 RUN systemctl enable dhcpd
 
-CMD ["sbin/init"]
+CMD ["sbin/init"]