shlib.sh: exit immediately with failure on missing Config

shlib.sh: exit immediately with failure on missing Config

When not using shlib_vars.sh to set the config shell variables such
as during the initial installation, if the $GIROCCO_CONF (which
defaults to Girocco::Config) module cannot be loaded to get the
configuration settings, exit immediately with an error.

While not normally an issue, if a custom configuration is being
used (now very easy by using a config.sh file) but the configuration
name has been set incorrectly, it's much saner to exit immediately
as soon as that's detected rather than accidentally continuing on.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>