preflight: Use read-only qemu:///system when calling virsh capabilities

crc's preflight check use virsh capabilities to make sure a qemu binary
supporting kvm is installed. It currently calls 'virsh capabilities'
which is apparently disabled on some setups.
This commit tries to use qemu:///system instead, but it only uses a
read-only connection as we don't know yet if the user is in the libvirt
group and has read/write access to qemu:///system.

This should fix #1994

Author: cfergeau

pkg/crc/preflight/preflight_checks_linux.go

@@ -88,7 +88,7 @@ func fixKvmEnabled() error {
 }
 
 func getLibvirtCapabilities() (*libvirtxml.Caps, error) {
-	stdOut, _, err := crcos.RunWithDefaultLocale("virsh", "capabilities")
+	stdOut, _, err := crcos.RunWithDefaultLocale("virsh", "--readonly", "--connect", "qemu:///system", "capabilities")
 	if err != nil {
 		return nil, fmt.Errorf("Failed to run 'virsh capabilities': %v", err)
 	}