net.tls_luasec: Expose method for loading a certificate

Further isolates LuaSec from Prosody core, with the ultimate goal of
allowing LuaSec to be replaced more easily.

core/certmanager.lua

@@ -6,7 +6,6 @@
 -- COPYING file in the source package for more information.
 --
 
-local ssl = require "ssl";
 local configmanager = require "prosody.core.configmanager";
 local log = require "prosody.util.logger".init("certmanager");
 local new_config = require"prosody.net.server".tls_builder;
@@ -98,7 +97,7 @@ local function index_certs(dir, files_by_name, depth_limit)
 				local firstline = f:read();
 				if firstline == "-----BEGIN CERTIFICATE-----" and lfs.attributes(find_matching_key(full), "mode") == "file" then
 					f:seek("set")
-					local cert = ssl.loadcertificate(f:read("*a"))
+					local cert = tls.load_certificate(f:read("*a"))
 					-- TODO if more than one cert is found for a name, the most recently
 					-- issued one should be used.
 					-- for now, just filter out expired certs

net/tls_luasec.lua

@@ -110,4 +110,5 @@ local luasec_has = ssl.config or {
 return {
 	features = luasec_has;
 	new_context = new_context,
+	load_certificate = ssl.loadcertificate;
 };