numpy runtime warnings

[gordon chung]

seeing this every so often with numpy 1.12.0:

/usr/lib64/python2.7/site-packages/numpy/core/_methods.py:135: RuntimeWarning: Degrees of freedom <= 0 for slice
  keepdims=keepdims)
/usr/lib64/python2.7/site-packages/numpy/core/_methods.py:127: RuntimeWarning: invalid value encountered in double_scalars
  ret = ret.dtype.type(ret / rcount)
2017-02-09 22:56:54.485 INFO gnocchi.cli [-] 17000 measurements bundles across 144 metrics wait to be processed.
/usr/lib64/python2.7/site-packages/numpy/core/_methods.py:135: RuntimeWarning: Degrees of freedom <= 0 for slice
  keepdims=keepdims)
/usr/lib64/python2.7/site-packages/numpy/core/_methods.py:127: RuntimeWarning: invalid value encountered in double_scalars
  ret = ret.dtype.type(ret / rcount)
/usr/lib64/python2.7/site-packages/numpy/core/_methods.py:135: RuntimeWarning: Degrees of freedom <= 0 for slice
  keepdims=keepdims)
/usr/lib64/python2.7/site-packages/numpy/core/_methods.py:127: RuntimeWarning: invalid value encountered in double_scalars
  ret = ret.dtype.type(ret / rcount)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/442395

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/442395
Committed: https://git.openstack.org/cgit/openstack/gnocchi/commit/?id=8040d06d3bd7e34d43d0c83057fda34521e6e165
Submitter: Jenkins
Branch: master

commit 8040d06d3bd7e34d43d0c83057fda34521e6e165
Author: Mehdi Abaakouk <email address hidden>
Date: Tue Mar 7 12:16:04 2017 +0100

    carbonara: remove numpy warning

    We ask scipy/numpy to compute std on serie with one timestamp. And numpy
    complains and return nan. Next we drop all nan.

    This change creates the list of timestamps that are not unique and then
    compute the std. numpy does not complain anymore and we don't have to
    remove nan.

    Closes-bug: #1663419
    Change-Id: Ie1ddd244e42dcac4f91f741f37a980e452f91845