Add DRP client config tests for secure proxy check
These tests make sure that client config plays well with
the secure proxy check.
Also, remove an unused function from DRP configurator.
BUG=
Committed:
https://crrev.com/8f0410ffae0fed84cba6f395c975deda14955c9b
Cr-Commit-Position: refs/heads/master@{#394590}