Refactor: PassiveDurabilityMonitor::throwException

The PDM throwException didn't use the PDM prefix and needed
a space between the vb and error.

Change-Id: I19e756c93504d4322a37a8ae61ba81c8799863eb
Reviewed-on: http://review.couchbase.org/112047
Reviewed-by: Dave Rigby <daver@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@couchbase.com>

engines/ep/src/durability/passive_durability_monitor.cc

@@ -528,5 +528,6 @@ void PassiveDurabilityMonitor::State::checkForAndRemovePrepares() {
 template <class exception>
 [[noreturn]] void PassiveDurabilityMonitor::throwException(
         const std::string& thrower, const std::string& error) const {
-    throw exception(thrower + error + vb.getId().to_string());
+    throw exception("PassiveDurabilityMonitor::" + thrower + " " +
+                    vb.getId().to_string() + " " + error);
 }