robust installation

[gerbaudo]

We often have errors when checking out the packages
(auth issues with kerberos, ssh timeouts etc.).
The installation script should be more robust, and try a
command N times before giving up. Ideally, it should also
parse the list of packages pulled in by
SUSYTools/python/install.py, and check those as well.
However, implementing this logic in bash is a pain in the
neck (I tried today when re-writing bash/setup_area.sh...).
I should rewrite the thing in python.
One thing that should be implemented is a separation
between the installation logic, and the list of tags. Just
put the tags in a separate json file (or in a separate py
file and eval it).