Fix master/slave handling in xenconsoled and qemu

Fix master/slave handling in xenconsoled and qemu

Fix a number of problems with the pty handling:

- make openpty() implementation work on Solaris
- set raw on the slave fd, not the master, as the master doesn't
  have a line discipline pushed on Solaris
- make sure we don't leak the slave fd returned from openpty()
- don't use the 'name' argument of openpty() as it's a security risk
- note behaviour of a zero read of the master on Solaris
- remove pointless tcget/setattr

Signed-off-by: John Levon <john.levon@sun.com>
Signed-off-by: Samuel Thibault <samuel.thibault@citrix.com>