qemu: Only one element of qemuPaths map is relevant

The qemuPaths field in qemuArchBase maps from machine type to the default
qemu path.  But, by the time we construct it, we already know the machine
type, so that entry ends up being the only one we care about.

So, collapse the map into a single path.  As a bonus, the qemuPath()
method can no longer fail.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

src/runtime/virtcontainers/qemu_arch_base.go

@@ -41,7 +41,7 @@ type qemuArch interface {
 	machine() govmmQemu.Machine
 
 	// qemuPath returns the path to the QEMU binary
-	qemuPath() (string, error)
+	qemuPath() string
 
 	// kernelParameters returns the kernel parameters
 	// if debug is true then kernel debug parameters are included
@@ -137,13 +137,13 @@ type qemuArch interface {
 
 type qemuArchBase struct {
 	qemuMachine           govmmQemu.Machine
+	qemuExePath           string
 	memoryOffset          uint32
 	nestedRun             bool
 	vhost                 bool
 	disableNvdimm         bool
 	dax                   bool
 	networkIndex          int
-	qemuPaths             map[string]string
 	kernelParamsNonDebug  []Param
 	kernelParamsDebug     []Param
 	kernelParams          []Param
@@ -242,13 +242,8 @@ func (q *qemuArchBase) machine() govmmQemu.Machine {
 	return q.qemuMachine
 }
 
-func (q *qemuArchBase) qemuPath() (string, error) {
-	p, ok := q.qemuPaths[q.qemuMachine.Type]
-	if !ok {
-		return "", fmt.Errorf("Unknown machine type: %s", q.qemuMachine.Type)
-	}
-
-	return p, nil
+func (q *qemuArchBase) qemuPath() string {
+	return q.qemuExePath
 }
 
 func (q *qemuArchBase) kernelParameters(debug bool) []Param {