Spaces are encoded correctly in variable IDs

[orenbm]

Summary

Variable IDs are not encoded at all so in case a user has a variable with spaces in it, we are not able to retrieve it.

We should use an encoding method that encodes spaces into "%20" as required
by the Conjur v5 server. We also encode slashes into "%2F" as required.

Steps to Reproduce

Steps to reproduce the behavior:

1. Create a Conjur variable with a space in its ID, and populate it.
2. Retrieve it with Puppet

Expected Results

Secret is retrieved

Actual Results (including error logs, if applicable)

404 error