[common] Add std::exception handler to ParsedInstance

[common] Add std::exception handler to ParsedInstance

When an exception derived from std::exception and not PlatformException
is thrown in webapi-plugins code, only the following error message was
logged:

HandleException(393) > Exception: Unknown exception

As std::exception inheritance is a very common practice, especially in
standard library, we add logging std::exception::what() message to make
debugging easier.

[Verification] An exception thrown from std::string is caught and its
what() message is logged properly.

Change-Id: I879ebe80b609cf26a7e68be822a783aa9ef145eb
Signed-off-by: Pawel Wasowski <p.wasowski2@samsung.com>