credential-factory: Avoid deadlock during unit tests

If a unit test times out while generating a private key (e.g. because of
a lack of entropy), this avoids a deadlock by still releasing the read
lock that'd prevent acquiring the write lock when plugins are unloaded.

Closes strongswan/strongswan#2850

src/libstrongswan/credentials/credential_factory.c

@@ -140,6 +140,8 @@ METHOD(credential_factory_t, create, void*,
 	this->recursive->set(this->recursive, (void*)level + 1);
 
 	this->lock->read_lock(this->lock);
+	/* push this in case of a timeout during unit tests */
+	thread_cleanup_push((thread_cleanup_t)this->lock->unlock, this->lock);
 	enumerator = this->constructors->create_enumerator(this->constructors);
 	while (enumerator->enumerate(enumerator, &entry))
 	{
@@ -159,7 +161,7 @@ METHOD(credential_factory_t, create, void*,
 		}
 	}
 	enumerator->destroy(enumerator);
-	this->lock->unlock(this->lock);
+	thread_cleanup_pop(TRUE);
 
 	if (!construct && !level)
 	{