qemurunner: Make create_socket() return data and use exceptions

qemurunner: Make create_socket() return data and use exceptions

So that create_socket() can be called more than once to create sockets,
it now returns the socket and port rather than setting class variables
directly.

create_socket() now only uses exceptions for errors, not the return
value from the function.

Signed-off-by: Randy Witt <randy.e.witt@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>