qemu: adjust the meaning of the -s (simple) flag

My primary use case for this flag is to fix booting with UEFI firmware
which can have problems when mixed with KVM, adding kexec into the mix
doesn't help matters either. The current version of OVMF can boot from
virtio drives just fine so that is now enabled and KVM is disabled.

So the -s option can also mean sloooooooow but boots!

build_library/qemu_template.sh

@@ -20,7 +20,7 @@ Options:
     -c FILE     Config drive as an iso or fat filesystem image.
     -a FILE     SSH public keys for login access. [~/.ssh/id_{dsa,rsa}.pub]
     -p PORT     The port on localhost to map to the VM's sshd. [2222]
-    -s          Safe settings: single simple cpu, ide disks.
+    -s          Safe settings: single simple cpu and no KVM.
     -h          this ;-)
 
 This script is a wrapper around qemu for starting CoreOS virtual machines.
@@ -131,11 +131,11 @@ fi
 
 # Start assembling our default command line arguments
 if [ "${SAFE_ARGS}" -eq 1 ]; then
-    disk_type="ide"
+    # Disable KVM, for testing things like UEFI which don't like it
+    set -- -machine accel=tcg "$@"
 else
-    disk_type="virtio"
     # Emulate the host CPU closely in both features and cores.
-    set -- -cpu host -smp "${VM_NCPUS}" "$@"
+    set -- -machine accel=kvm -cpu host -smp "${VM_NCPUS}" "$@"
 fi
 
 # ${CONFIG_DRIVE} or ${CONFIG_IMAGE} will be mounted in CoreOS as /media/configdrive
@@ -146,11 +146,11 @@ if [ -n "${CONFIG_DRIVE}" ]; then
 fi
 
 if [ -n "${CONFIG_IMAGE}" ]; then
-    set -- -drive if=${disk_type},file="${CONFIG_IMAGE}" "$@"
+    set -- -drive if=virtio,file="${CONFIG_IMAGE}" "$@"
 fi
 
 if [ -n "${VM_IMAGE}" ]; then
-    set -- -drive if=${disk_type},file="${SCRIPT_DIR}/${VM_IMAGE}" "$@"
+    set -- -drive if=virtio,file="${SCRIPT_DIR}/${VM_IMAGE}" "$@"
 fi
 
 if [ -n "${VM_KERNEL}" ]; then
@@ -173,7 +173,6 @@ fi
 qemu-system-x86_64 \
     -name "$VM_NAME" \
     -m ${VM_MEMORY} \
-    -machine accel=kvm:tcg \
     -net nic,vlan=0,model=virtio \
     -net user,vlan=0,hostfwd=tcp::"${SSH_PORT}"-:22,hostname="${VM_NAME}" \
     "$@"