Fix more problems with "/usr/bin/env python" picking python3.

Open files in 'rb' (read binary) mode to prevent useless default utf8
encoding in python3, without breaking python2 compatibility.

Reported-by: Tharre <tharre3@gmail.com>

docs/cookbook/container/default.sha256.do

@@ -8,7 +8,7 @@ subprocess.check_call([
 ], close_fds=False)
 
 h = hashlib.sha256()
-f = open(sys.argv[2])
+f = open(sys.argv[2], 'rb')
 while 1:
     b = f.read(65536)
     if not b: break

docs/cookbook/container/fileids.py

@@ -6,14 +6,14 @@ for name in sys.stdin:
     st = os.lstat(name)
     if stat.S_ISREG(st.st_mode):
         h = hashlib.sha256()
-        f = open(name)
+        f = open(name, 'rb')
         while 1:
             b = f.read(65536)
             if not b: break
             h.update(b)
         digest = h.hexdigest()
     elif stat.S_ISLNK(st.st_mode):
-        digest = hashlib.sha256(os.readlink(name)).hexdigest()
+        digest = hashlib.sha256(os.readlink(name).encode('utf8')).hexdigest()
     else:
         digest = '0'
     print('%s %07o-%s-%s-%s' % (