ZenCommand can fail on non-numeric values

[cluther]

ZenCommand can fail when badly formed numeric values are returned from the command. Examples of these values include "1-1" and "1.1.1".

When these bad values are encountered a ValueError exception is thrown and all of the returned values, even properly formatted ones are lost.

Traceback (most recent call last):
  File "/opt/zenoss/lib/python/twisted/internet/process.py", line 673, in maybeCallProcessEnded
    self.proto.processEnded(failure.Failure(e))
  File "/opt/zenoss/Products/ZenRRD/zencommand.py", line 138, in processEnded
    d.callback(self)
  File "/opt/zenoss/lib/python/twisted/internet/defer.py", line 239, in callback
    self._startRunCallbacks(result)
  File "/opt/zenoss/lib/python/twisted/internet/defer.py", line 304, in _startRunCallbacks
    self._runCallbacks()
--- <exception caught here> ---
  File "/opt/zenoss/lib/python/twisted/internet/defer.py", line 317, in _runCallbacks
    self.result = callback(self.result, *args, **kw)
  File "/opt/zenoss/Products/ZenRRD/zencommand.py", line 486, in finished
    self.parseResults(cmd)
  File "/opt/zenoss/Products/ZenRRD/zencommand.py", line 552, in parseResults
    value = float(parts.group(3))
exceptions.ValueError: invalid literal for float(): 1.3.6.1.2.1.25.2.1.1

[cluther]

(In [7086]) * Fixes #2157.