allow filtering driver integration tests

Signed-off-by: Evan Hazlett <ejhazlett@gmail.com>

integration-test/test_vars.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
+	"strings"
 )
 
 type (
@@ -18,6 +19,16 @@ var (
 )
 
 func init() {
+	// allow filtering driver tests
+	if machineTests := os.Getenv("MACHINE_TESTS"); machineTests != "" {
+		tests := strings.Split(machineTests, " ")
+		for _, test := range tests {
+			mcn := MachineDriver{
+				name: test,
+			}
+			machineTestDrivers = append(machineTestDrivers, mcn)
+		}
+	} else {
 		machineTestDrivers = []MachineDriver{
 			MachineDriver{
 				name: "virtualbox",
@@ -26,6 +37,9 @@ func init() {
 				name: "digitalocean",
 			},
 		}
+	}
+
+	// find machine binary
 	if machineBin := os.Getenv("MACHINE_BINARY"); machineBin != "" {
 		machineBinary = machineBin
 	} else {