Response with internal error on invalid Chassis path

Added verification of chassis path in case if received path is
invalid. Response with internal error on wrong format of a path.

Tested:
 - Verify if chassis collection is filled properly
 - Verify if internal error is returned on wrong path
 - RedfishServiceValidator.py passes

Signed-off-by: Wludzik, Jozef <jozef.wludzik@intel.com>
Change-Id: Ibe2b9a12d0a5c2c05c9db502b65d2196851352b5