Fix py3 issues

- Update popen to use universal_newlines=True to enable newlines
  for calls that we parse or consume output for. Without universal_newlines=True,
  the output is treated as bytes under python3
  which leads to issues later where we are using it as
  strings.
- The division operator in Python 3 results in a float, not an integer
  like in Python 2. Use the truncation division operator instead.
- Use python builtins since the behavior of round has changed between
  python2 and python3.
  (https://docs.python.org/3/whatsnew/3.0.html#builtins)

Story: 2006796
Task: 42695

Signed-off-by: Charles Short <charles.short@windriver.com>
Change-Id: I9c9a4fdfd8a65cf6a3034a2c80c3a620ab138d22
(cherry picked from commit 9ced50cf38)

tools/storage-topology/storage-topology/storage_topology/exec/storage_topology.py

@@ -29,6 +29,7 @@ import textwrap
 import keyring
 import subprocess
 import math
+from builtins import round
 from prettytable import PrettyTable
 from cgtsclient.common import utils
 from cgtsclient import client as cgts_client
@@ -145,7 +146,7 @@ def get_system_creds():
 
     proc = subprocess.Popen(['bash', '-c',
                              'source /etc/platform/openrc && env'],
-                            stdout=subprocess.PIPE)
+                            stdout=subprocess.PIPE, universal_newlines=True)
 
     for line in proc.stdout:
         key, _, value = line.partition("=")
@@ -180,7 +181,7 @@ def convert_to_readable_size(size, orig_unit='B'):
     if unitIndex > 5:
         unitIndex = 5
     sizer = math.pow(1024, unitIndex)
-    newsize = round(size / sizer, 2)
+    newsize = round(size // sizer, 2)
     return "%s %s" % (newsize, units[unitIndex])