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.

* To reduce the image dimension, two RUN commands are merged in one single layer.
* All packages are installed with a single command.
* remove cern and garr mirrors
* the clean commands are the last instructions in the layer
* sudo is installed only in the dockerfile

To create the vscode user, the provide_user.sh script is used. With this script the comand line appearance is improved with colors and branch informations

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