nsswitch: add support for the automount database

[compnerd]

automount is a valid database for the name switch service. This allows processing the database entry in the configuration. The service now starts up rather than erroring out as it is unable to process the configuration.

[compnerd]

I agree that discarding unknown databases seems reasonable (and potentially even for the ones that we know about but do not support, i.e. everything but passwd and group). But, that would be a much larger change and this does enable additional files to be processed. A subsequent change to do that seems reasonable.

[compnerd]

@ericonr ping?

[compnerd]

@ericonr ping?

[ericonr]

Please squash the commits into a single one and mention in the commit message that this should instead implement something to ignore unknown entries, instead of trying to parse them.

[compnerd]

Sure; done! Sorry about the delay for the request.