Raspbian has shipped many 3rd-party python wheels through
https://www.piwheels.org/simple including tensorflow. This made
building docker images much easier.

This patch upgrades the following 3rd-party packages:
- https://bootstrap.pypa.io/get-pip.py
- numpy==1.15.0
- tensorflow==1.9.0

Deb package python-numpy and python-scipy were removed to avoid conficts
reported by pip install.

Deb package libatlas3-base was added. Because it was needed by numpy.

Signed-off-by: Liu Qun <[email protected]>

This enables cross-building from x86 host.

Signed-off-by: Liu Qun <[email protected]>

Signed-off-by: Liu Qun <[email protected]>