[Geneva Metrics Exporter] - Add support for abstract socket

[lalitb]

Add support for abstract socket. From man-page:

   *  abstract: an abstract socket address is distinguished (from a
          pathname socket) by the fact that sun_path[0] is a null byte
          ('\0').  The socket's address in this namespace is given by
          the additional bytes in sun_path that are covered by the
          specified length of the address structure.  (Null bytes in the
          name have no special significance.)  The name has no
          connection with filesystem pathnames.  When the address of an
          abstract socket is returned, the returned addrlen is greater
          than sizeof(sa_family_t) (i.e., greater than 2), and the name
          of the socket is contained in the first (addrlen -
          sizeof(sa_family_t)) bytes of sun_path.

The changes are

• Remove dependency of URLParser to parse the connection string for UDS, Abstract socket and ETW. As URLParser is not able to parse the abstract socket, and parsing logic is very straightforward for these transport mechanisms.
  • Add unit-test case to test abstract sockets.
  • Add stress test for Linux.