[LNT] Python 3 support: adapt secret computation

[thopre]

Summary

Computation of the secret when it is not supplied on the command line
involves passing a string constructed with str to the sha1 function.
However that function expects binary data which is a different type in
Python3. This commit uses the bytes constructor as an additional step to
convert from text to binary data.

[thopre]

Ping?

[hubert.reinterpretcast]

lnt/lnttool/create.py

141–146

Being no security expert, I am not sure about the patch. I do see that getrandbits is documented as not being for security purposes, but I think we can do the Python 3 support without changing the status quo of the "security".

With the future package:

from builtins import bytes
hashlib.sha1(bytes(str(random.getrandbits(256)), encoding='ascii')).hexdigest()

[thopre]

Use approach suggested by Hubert to adapt the existing code rather than use a new way of generating random bits to not change the security strength of the code.

[hubert.reinterpretcast]

LGTM.

[thopre]

Fix mypy warning

lnt/lnttool/create.py

def action_create(instance_path, name, config, wsgi, tmp_dir, db_dir,
                   profile_dir, default_db, secret_key, hostname, hostsuffix,
                   show_sql):
     """create an LLVM nightly test installation
 
 \b
 * INSTANCE_PATH should point to a directory that will keep
 LNT configuration.
     """
+    from builtins import bytes
     from .common import init_logger
     import hashlib
     import lnt.server.db.migrate
     import lnt.server.db.util
     import lnt.testing
     import logging
     import os
     import random
     import sys
 
     init_logger(logging.INFO if show_sql else logging.WARNING,
                 show_sql=show_sql)
 
     basepath = os.path.abspath(instance_path)
     if os.path.exists(basepath):
         raise SystemExit("error: invalid path: %r already exists" % basepath)
 
     hosturl = "http://%s/%s" % (hostname, hostsuffix)
 
     python_executable = sys.executable
     cfg_path = os.path.join(basepath, config)
     tmp_path = os.path.join(basepath, tmp_dir)
     wsgi_path = os.path.join(basepath, wsgi)
     schemas_path = os.path.join(basepath, "schemas")
-    secret_key = (secret_key or
-                  hashlib.sha1(str(random.getrandbits(256))).hexdigest())
+    secret_key = (
+        secret_key or
+        hashlib.sha1(
+            bytes(str(random.getrandbits(256)), encoding="ascii")
+        ).hexdigest()
+    )
 
     os.mkdir(instance_path)
     os.mkdir(tmp_path)
     os.mkdir(schemas_path)
 
     # If the path does not contain database type, assume relative path.
     if lnt.server.db.util.path_has_no_database_type(db_dir):
         db_dir_path = os.path.join(basepath, db_dir)