Introduce a virQEMUDriverConfigPtr object

Currently the virQEMUDriverPtr struct contains an wide variety
of data with varying access needs. Move all the static config
data into a dedicated virQEMUDriverConfigPtr object. The only
locking requirement is to hold the driver lock, while obtaining
an instance of virQEMUDriverConfigPtr. Once a reference is held
on the config object, it can be used completely lockless since
it is immutable.

NB, not all APIs correctly hold the driver lock while getting
a reference to the config object in this patch. This is safe
for now since the config is never updated on the fly. Later
patches will address this fully.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

tests/qemuxml2argvdata/qemuxml2argv-graphics-vnc-tls.args

@@ -2,4 +2,4 @@ LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test \
 SASL_CONF_DIR=/root/.sasl2 QEMU_AUDIO_DRV=none /usr/bin/qemu -S -M pc -m 214 \
 -smp 1 -monitor unix:/tmp/test-monitor,server,nowait -no-acpi -boot c -usb -hda \
 /dev/HostVG/QEMUGuest1 -net none -serial none -parallel none -vnc \
-127.0.0.1:3,tls,x509verify=/etc/pki/tls/qemu,sasl
+127.0.0.1:3,tls,x509verify=/etc/pki/libvirt-vnc,sasl