tools: make pem file writable by owner before tryting to write

A PEM file might not be writable by the owner when it should be written
(e.g. on Windows), so we have to ensure the file has write permissions
before doing so

acertmgr/tools.py

@@ -10,6 +10,7 @@ import base64
 import datetime
 import io
 import os
+import stat
 import sys
 import traceback
 
@@ -186,6 +187,11 @@ def read_pem_file(path, key=False, csr=False):
 
 # @brief write cert data to PEM formatted file
 def write_pem_file(crt, path, perms=None):
+    if hasattr(os, 'chmod') and os.path.exists(path):
+        try:
+            os.chmod(path, os.stat(path).st_mode | stat.S_IWRITE)
+        except OSError:
+            log('Could not make file ({0}) writable'.format(path), warning=True)
     with io.open(path, "w") as f:
         f.write(convert_cert_to_pem_str(crt))
     if perms: