made dockerfile build. was breaking in two places:

1) installing packages:
Step 3 : RUN apt-get install -y sudo openssh-server curl lsb-release git
 ---> Running in 03ef4028544a
Reading package lists...
Building dependency tree...
Reading state information...
Package openssh-server is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

Package lsb-release is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  base-files

E: Unable to locate package sudo
E: Package 'openssh-server' has no installation candidate
E: Unable to locate package curl
E: Package 'lsb-release' has no installation candidate
E: Unable to locate package git

2) Creating symlink that already existed:
Step 6 : RUN ln -s /bin/true /sbin/initctl
 ---> Running in 933b6238e344
ln: failed to create symbolic link `/sbin/initctl': File exists

Soutions are to simply add an apt-get update before installing any packages and to use -f flag when creating a symlink to unlink if exists and relink.