'scikit-learn' requires 'numpy' and 'scipy' packages. Which take long
time to build.
We need 'numpy' for nova image but can ignore rest (they are needed by
'monasca_analytics' project we do not use).
On x86-64 architecture all those packages come as binaries from Pypi.
Change-Id: I36b6ca9d094f83d48e7fa41a7818441169bd04e6