res/res_corosync: Always decline module load, instead of failing

res/res_corosync: Always decline module load, instead of failing

Returns a 'failure' from the module load routine indicates to Asterisk
that it should abort loading completely. This is rarely - in fact,
really, never - a good option. Aborting load of Asterisk from a dynamic
module implies that the core, and the rest of the dynamic modules, don't
matter: we should abandon all processing.

res_corosync is really not that important.

This patch updates the module such that, if it fails to load, it
politely declines (emitting ERROR messages along the way), and allows
Asterisk to continue to function.

Note that this issue was keeping Asterisk unit tests from running on
certain build agents.

Change-Id: I252249e81fb9b1a68e0da873f54f47e21d648f0f