pg_hba should validate that target is an absolute path

[mcanevet]

If you use pg_hba without specifying a target, it fails with:

Could not evaluate: private method `chomp' called for nil:NilClass

Because of:

def self.file(resource)
    ...
    file = resource[:target]
    file.chomp("/")
end

in pg_hba augeas provider.

I think it should be validated in the type to fail properly.