Ask password when encrypted disk image is used (Laurent Vivier)

This patch repairs the management of encrypted disk images and allows to
enter the password.

Changelog:
v2:
- move read_password() before do_loadvm()
- really start monitor if output is stdio.

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@4976 c046a42c-6fe2-441c-8c8c-71466251a162
