Use monotonic library to avoid finding monotonic time function

That library already does this same/equivalent search and
ensures that a monotonically increasing time is made available
so we can just avoid looking around for it ourselves.

Depends-On: I0f07858e96ea3baf46f8a453e253b9ed29c7f7e2

Depends-On: I33bd2d9dff9cb7dc1a50177db7286b7317966784

Change-Id: Idd2109c8947d10cdbd62c53998ab2e31382e8633

oslo_utils/timeutils.py

@@ -23,6 +23,7 @@ import time
 
 from debtcollector import removals
 import iso8601
+from monotonic import monotonic as now  # noqa
 from pytz import timezone
 import six
 
@@ -35,19 +36,6 @@ PERFECT_TIME_FORMAT = _ISO8601_TIME_FORMAT_SUBSECOND
 
 _MAX_DATETIME_SEC = 59
 
-# Use monotonic time in stopwatches if we can get at it...
-#
-# PEP @ https://www.python.org/dev/peps/pep-0418/
-try:
-    now = time.monotonic
-except AttributeError:
-    try:
-        # Try to use the pypi module if it's available (optionally...)
-        from monotonic import monotonic as now
-    except (AttributeError, ImportError):
-        # Ok fallback to the non-monotonic one...
-        now = time.time
-
 
 @removals.remove(
     message="use datetime.datetime.isoformat()",

requirements.txt

@@ -12,6 +12,7 @@ Babel>=1.3
 six>=1.9.0
 iso8601>=0.1.9
 oslo.i18n>=1.5.0 # Apache-2.0
+monotonic>=0.1 # Apache-2.0
 pytz>=2013.6
 netaddr>=0.7.12
 netifaces>=0.10.4