sockets: change inet_connect() to support nonblock socket
Add a bool argument to inet_connect() to assign if set socket
to block/nonblock, and delete original argument 'socktype'
that is unused.
Add a new argument to inet_connect()/inet_connect_opts(),
to pass back connect error by error class.
Retry to connect when -EINTR is got. Connect's successful
for nonblock socket when following errors are got, user
should wait for connecting by select():
-EINPROGRESS
-EWOULDBLOCK (win32)
-WSAEALREADY (win32)
Change nbd, vnc to use new interface.
Signed-off-by: Amos Kong <akong@redhat.com> Reviewed-by: Orit Wasserman <owasserm@redhat.com> Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>