Support for Windows paths in the source position of the volume mounts

There are 2 things added. First there is added support for handling drive
letters while doing value split. If drive letter is detected, then max number
of elements will be increased by one, but then first two will be concatenated
to reconstruct the path. Second part is basic, but working, conversion of Windows
path to Unix path to be used, when target path is not explicitly specified.

Signed-off-by: Arthur Sengileyev <arthur.sengileyev@gmail.com>

pkg/machine/qemu/machine_unix.go

@@ -6,6 +6,7 @@ package qemu
 import (
 	"bytes"
 	"fmt"
+	"strings"
 	"syscall"
 
 	"golang.org/x/sys/unix"
@@ -31,3 +32,14 @@ func checkProcessStatus(processHint string, pid int, stderrBuf *bytes.Buffer) er
 	}
 	return nil
 }
+
+func pathsFromVolume(volume string) []string {
+	return strings.SplitN(volume, ":", 3)
+}
+
+func extractTargetPath(paths []string) string {
+	if len(paths) > 1 {
+		return paths[1]
+	}
+	return paths[0]
+}