Add gvm_auto_{install,use} in $GVM_DIR/etc/config

[dsyer]

These flags are consulted when gvm is asked to use an uninstalled version
or to install an unused version. User is prompted for a response
by default but this can be overridden by adding these flags to
the confg, e.g.

Fixes #101

$ echo gvm_auto_install=Y >> $GVM_DIR/etc/config
$ echo gvm_auto_use=Y >> $GVM_DIR/etc/config
$ gvm use groovy 1.8.8
... (installs and uses without prompting)

[dsyer]

Makes sense. New patch (as a separate commit) is available.

[pledbrook]

Maybe I just like being difficult, but the two separate options make sense to me. Would anyone configure each differently? Maybe not, but I learned not to second-guess users a long time ago. Plus I find the gvm_auto name confusing 😄

[marc0der]

@pledbrook I like to configure things only when the requirement is there. Clearly there is a requirement for the config, but not for both individually. I again have worked on projects where everything was configured to death, resulting in an extremely difficult to maintain (and deploy!) code base. Since then I've learnt to do only what is required.

Thinking we should keep it as one config, but agree that the name is a bit misleading (sorry @dsyer :-X)

[dsyer]

OK what would you suggest (gvm_auto_use_or_install_depending_on_the_context)?

[marc0der]

continuous_integration_environment or auto_answer perhaps?