Make dummy cpu_load_percent also ThreadedSegment

It is the easiest way to make documentation identical when created on a system 
with and without psutil module and deduplicate docstrings

powerline/segments/common.py

@@ -573,15 +573,6 @@ try:
 
 		def render(self, cpu_percent, format='{0:.0f}%', **kwargs):
 			return format.format(cpu_percent)
-
-	cpu_load_percent = with_docstring(CPULoadPercentSegment(),
-	'''Return the average CPU load as a percentage.
-
-	Requires the ``psutil`` module.
-
-	:param str format:
-		Output format. Accepts measured CPU load as the first argument.
-	''')
 except ImportError:
 	def _get_bytes(interface):  # NOQA
 		with open('/sys/class/net/{interface}/statistics/rx_bytes'.format(interface=interface), 'rb') as file_obj:
@@ -599,16 +590,35 @@ except ImportError:
 	def _get_user(segment_info):  # NOQA
 		return segment_info['environ'].get('USER', None)
 
-	def cpu_load_percent(pl, measure_interval=.5):  # NOQA
+	class CPULoadPercentSegment(ThreadedSegment):  # NOQA
+		interval = 1
+
+		@staticmethod
+		def startup(**kwargs):
+			pass
+
+		@staticmethod
+		def start():
+			pass
+
+		@staticmethod
+		def shutdown():
+			pass
+
+		@staticmethod
+		def render(cpu_percent, pl, format='{0:.0f}%', **kwargs):
+			pl.warn('psutil package is not installed, thus CPU load is not available')
+			return None
+
+
+cpu_load_percent = with_docstring(CPULoadPercentSegment(),
 '''Return the average CPU load as a percentage.
 
 Requires the ``psutil`` module.
 
-		:param float measure_interval:
+:param str format:
-			interval used to measure CPU load (in seconds)
+	Output format. Accepts measured CPU load as the first argument.
-		'''
+''')
-		pl.warn('psutil package is not installed, thus CPU load is not available')
-		return None
 
 
 username = False