lib terraform: preserve file mode when copying over

If someone wants to cache providers they will be executable and not
match the expected file view pattern. It's best to preserve permissions
when possible

lib/terraform/local.go

@@ -52,6 +52,11 @@ func CopyDir(stack resource.Stack, dst string, resource resource.Resource) error
 }
 
 func replaceVariablesInFile(srcFile, dstFile string, resource resource.Resource, stack resource.Stack) error {
+	fileInfo, err := os.Stat(srcFile)
+	if err != nil {
+		return oops.Wrapf(err, "error accessing file %s", srcFile)
+	}
+
 	content, err := ioutil.ReadFile(srcFile)
 	if err != nil {
 		return err
@@ -76,5 +81,5 @@ func replaceVariablesInFile(srcFile, dstFile string, resource resource.Resource,
 		return oops.Errorf("Region needs to be set on stack if performing substitution")
 	}
 
-	return ioutil.WriteFile(dstFile, []byte(updatedContent), 0644)
+	return ioutil.WriteFile(dstFile, []byte(updatedContent), fileInfo.Mode())
 }