Set focus to monitor to ask password if line is multiplexed (Laurent Vivier)

Set focus to monitor to ask password if line is	multiplexed (Laurent Vivier)

This patch allows to display the "Password:" prompt if we use encrypted
disk with "-nographic" option.

It also modifies management of "-nographic" to not override user's
choices for "-serial", "-parallel" and "-monitor".

When qemu has to ask a password with "-nographic" with a multiplexed
serial interface, it forces the focus to the monitor and restore
original focus after.

Signed-off-by: Laurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@4979 c046a42c-6fe2-441c-8c8c-71466251a162