qemuProcessStart is going to be split in three parts: qemuProcessInit,
qemuProcessLaunch, and qemuProcessFinish so that migration Prepare phase
can insert additional code in the process. qemuProcessStart will be a
small wrapper for all other callers.

qemuProcessInit prepares the domain up to the point when priv->qemuCaps
is initialized.
Signed-off-by: NJiri Denemark <jdenemar@redhat.com>