Provide certificate path to Salt Vault configuration

Summary:
Requests library uses the certifi package, which hardcodes a specific
bundle of certificates.

Specify the path to the CA root certificate used by Vault certificate.
Salt will use that one to check it.

Reference: https://docs.saltproject.io/en/latest/ref/modules/all/salt.modules.vault.html

Test Plan: Tested on Dwellers

Reviewers: DorianWinty

Reviewed By: DorianWinty

Differential Revision: https://devcentral.nasqueron.org/D2798