Merge pull request #29 from sharifelgamal/master

don't panic if hyper-v isn't enabled

Author: afbjorklund

drivers/hyperv/powershell.go

@@ -61,7 +61,7 @@ func hypervAvailable() error {
 	}
 
 	resp := parseLines(stdout)
-	if resp[0] != "Hyper-V" {
+	if resp == nil || len(resp) == 0 || resp[0] != "Hyper-V" {
 		return ErrNotInstalled
 	}