Adds https support for metadata agent

Adds two configure options to support https client for metadata proxy
* auth_insecure: turn off verification of the certificate for ssl, or
* auth_ca_cert: CA cert to check against with for ssl.

Change-Id: I3ffb86ae9ce31931436a4e13957aae30eebf9d92
Closes-Bug: #1263872
Merge "Adds https support for metadata agent"