res_stir_shaken: Fix compilation for CentOS7 (openssl 1.0.2)

res_stir_shaken:  Fix compilation for CentOS7 (openssl 1.0.2)

* OpenSSL 1.0.2 doesn't support X509_get0_pubkey so we now use
  X509_get_pubkey.  The difference is that X509_get_pubkey requires
  the caller to free the EVP_PKEY themselves so we now let
  RAII_VAR do that.
* OpenSSL 1.0.2 doesn't support upreffing an X509_STORE so we now
  wrap it in an ao2 object.
* OpenSSL 1.0.2 doesn't support X509_STORE_get0_objects to get all
  the certs from an X509_STORE and there's no easy way to polyfill
  it so the CLI commands that list profiles will show a "not
  supported" message instead of listing the certs in a store.

Resolves: #676
(cherry picked from commit 4cb56ccd28a836828409de648f195bc9ba6a6f34)