[vpython] Incorporate interpreter path/hash.

vpython/python/find.go

 // Copyright 2017 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package python
 
 import (
         "os/exec"
 
         "github.com/luci/luci-go/common/errors"
@@ skipping 27 matching lines @@
                         if e, ok := err.(*exec.Error); ok && e.Err == exec.ErrNotFound {
                                 // Not found is okay.
                                 continue
                         }
                         return nil, errors.Annotate(err).Reason("failed to search PATH for: %(interp)q").
                                 D("interp", s).
                                 Err()
                 }
 
                 i := Interpreter{Python: p}
+                if err := i.Normalize(); err != nil {
+                        return nil, err
+                }
+
                 iv, err := i.GetVersion(c)
                 if err != nil {
                         return nil, errors.Annotate(err).Reason("failed to get version for: %(interp)q").
-                                D("interp", p).
+                                D("interp", i.Python).
                                 Err()
                 }
                 if vers.IsSatisfiedBy(iv) {
                         return &i, nil
                 }
         }
 
         return nil, errors.New("no Python found")
 }