All the file in assets used tu build the devcontainer are moved in library-script.

Modify the Dockerfile COPY directory

The yum install commands were copy-&-paste from the 3  original images.
Now all the repo are installed first; then, they are followed by all the other packages merged together in a single yum install command.

To create the image defined in this dockerfile, we've merged three differend images:
 * storm2/build/base
 * storm2/build/ngx-voms-build [issue-17]
 * storm2/ngx_http_voms_module/.devcontainer
Each image has this own 'yum install' command with the packages needed for that layer.

With this commit, all the packages are installed in a single layer to reduce the image dimension.
All the 'yum install' commands are grouped in the setup.sh script.

The script can be used both for the devcontainer and for the continuous
integration.