Add mig-strategy flag to mps-control-daemon

This change makes the handling of the MIG strategy consistent with
GFD and the device plugin.

This also removes the need to explicitly check for nil values when querying
this value.

Signed-off-by: Evan Lezar <elezar@nvidia.com>

cmd/mps-control-daemon/main.go

@@ -66,6 +66,12 @@ func main() {
 			Destination: &config.configFile,
 			EnvVars:     []string{"CONFIG_FILE"},
 		},
+		&cli.StringFlag{
+			Name:    "mig-strategy",
+			Value:   spec.MigStrategyNone,
+			Usage:   "the desired strategy for exposing MIG devices on GPUs that support it:\n\t\t[none | single | mixed]",
+			EnvVars: []string{"MIG_STRATEGY"},
+		},
 	}
 	c.Flags = config.flags