(#21817) Ignore duplicate certs

Previously, SSL connections initiated by the puppet agent on windows, e.g
puppet module install, would cause the agent to terminate if the 'Root' store
on Windows contained duplicate certificates.

This commit ensures that we only add unique certificates to the X509 store.
Also, if we fail to add a certificate to the store, we issue a warning and
continue.
Merge pull request #1916 from joshcooper/ticket/master/21817-ignore-duplicate-certs

(#21817) Ignore duplicate certs