Change multipart boundary

While base64 should generate a valid boundary, some implementations balk at /.

Change to urlsafe alphabet.

Also, technically our boundary was potentially too big depending on readings of standards, reduce so that under any reading we are less than 70 characteres even including added '--' characters.

Change-Id: Id887a03eeb63a8d2bef000ae5e7365d269349906

pyghmi/util/webclient.py

@@ -99,7 +99,7 @@ class FileDownloader(threading.Thread):
 
 def get_upload_form(filename, data, formname, otherfields, boundary=BND):
     if not boundary:
-        boundary = base64.b64encode(os.urandom(54))[:70]
+        boundary = base64.urlsafe_b64encode(os.urandom(54))[:66]
     ffilename = filename.split('/')[-1]
     if not formname:
         formname = ffilename