preflight: Warn when libvirtd is not running

CodeReady Containers assumes libvirtd to be auto started at boot time,
or at least to be running when `crc start` is called.
The code to automatically enable libvirtd has been removed as it's quite
complicated to do automatically, and indicates that the system has been
manually modified by the user.
This commit adds a warning to let the user know some extra configuration
steps may be needed.

Author: cfergeau

pkg/crc/preflight/preflight_checks_linux.go

@@ -185,9 +185,11 @@ func checkLibvirtServiceRunning() error {
 	}
 	stdOut, _, err := crcos.RunWithDefaultLocale(path, "is-active", "libvirtd")
 	if err != nil {
+		logging.Warnf("No active (running) libvirtd systemd unit could be found - make sure one of libvirt systemd unit could be found - make sure one of libvirt systemd units is enabled so that it's autostarted at boot time.")
 		return fmt.Errorf("Failed to check if libvirtd service is active")
 	}
 	if strings.TrimSpace(stdOut) != "active" {
+		logging.Warnf("No active (running) libvirtd systemd unit could be found - make sure one of libvirt systemd unit could be found - make sure one of libvirt systemd units is enabled so that it's autostarted at boot time.")
 		return fmt.Errorf("libvirtd.service is not running")
 	}
 	logging.Debug("libvirtd.service is already running")