Default path for augments inputs should be relative to sys.policy_entry instead of sys.inputdir

While adding documentation for the inputs key in Augments I noticed that file paths are relative to sys.inputdir. I think that it makes more sense for inputs defined from augments to be relative to sys.policy_entry.

With the current behaviour I would not expect that policy loaded via Augments inputs would be validated as expected in a CI environment. When testing policy, it's common to use cf-promises with -f, e.g. cf-promise -f ./promises.cf. This is very likely to be wrong unless the policy is being checked in sys.inputdir (~/.cfagent/inputs or /var/cfengine/inputs, depending if the user is or isn't root. Using a fully qualified path makes testing the policy from temporary locations problematic.