Get the named property value of an instance identified by reference op.
Arguments are the client object pointer cl, an ObjectPath object pointer op with the namespace and classname
to identify the instance, a pointer to a string with the property name to get in name, and rc which returns
the operation status (suppressed when NULL).
When successful the CMCIClientFT.getProperty() function returns a CMPIData object with the instance property
value and sets a successful operation status code in rc. When unsuccessful it returns the CMPIStatus object
with sets an operation status error code and corresponding error string.