No error control when not finding the config file

[fjaviernieto]

When the Zabbix probes are not able to find the configuration file in the expected location (/etc/zabbix/) the PropertiesManager class fails and no property can be loaded. Since the jar file already contains a default config file, the class should take that default file in case the customized user config file cannot be found.
On the other hand, some control mechanism should take into account the configuration properties could be empty.

[fjaviernieto]

Updated modifications in the PropertiesManager class, for Heapster and OCCI probes. Problem is solved now.