Add python 3.8 support and deprecate python 3.5

[mtreinish]

Summary

This commit adds support for running aqua under python 3.8. It does
this by adding the trove classifiers to the package metadata and adding
a test job for python 3.8 At the same time this commit starts the
deprecation window for python 3.5. Python 3.5 goes end of life by
upstream python in Sept. 2020. We should give our users running with
python 3.5 (which is about 10% of qiskit users this year based on pypi
data) fair notice that when upstream python stops supporting it we do as
well. Corresponding to this change, terra is going to start raising a
warning when anything from qiskit.* is imported, see:
Qiskit/qiskit#3268

Details and comments

Python's documented branch support status and EoL dates are listed here:
https://devguide.python.org/#branchstatus

Waiting on upstream dependencies:

• h5py Linux/ macOS wheels for python 3.8 h5py/h5py#1410
• pycsf Add Python 3.8 wheels to pypi pyscf/pyscf#438
• qiskit-terra Add python 3.8 support and deprecate python 3.5 Qiskit/qiskit#3268
• qiskit-aer Add python 3.8 support and deprecate python 3.5 Qiskit/qiskit-aer#428
• qiskit-ignis Add python 3.8 support and deprecate python 3.5 qiskit-ignis#298

[mtreinish]

It'd be good to determine if all of aqua's dependencies support python 3.8 before merging this, but since we don't run ci for anything but python 3.6 it's hard to tell that without manually testing locally. (the other elements are doing this in ci)

[manoelmarques]

Running a travis for python 3.8 and also trying on MacOS, the following dependencies don't install due to lack of a proper python 3.8 wheel file: pyscf, h5py and cvxopt.

I found issues for h5py and cvxopt:
h5py/h5py#1410
cvxopt/cvxopt#77

The pycsf library build fails because it can't find libcint library.
The cvxopt library build fails because it can't find the SuiteSparse library.
The h5py library build fails because it can't find a pre-built libhdf5.so library.

It seems to me that Aqua is not ready for python 3.8 until python 3.8 wheel files are provided for those libraries in Pypi or we would need instructions written on how the user can build and install those libraries for his OS before installing Aqua, assuming their code is ready for python 3.8

[mtreinish]

Well for cvxopt we should be moving away from that for license compatibility reasons (see Qiskit/qiskit-aer#430 and qiskit-community/qiskit-ignis#300). @dongreenberg said there is a plan for switching to sklearn which will take care of that here.

But for the other ones that's definitely true I'll put this on hold and update the PR summary. It's probably worth pointing out that terra, aer, and ignis are blocked on supporting python 3.8 for one reason or another too. (terra on macOS also tripped a regression introduced in python3.8) so it might be a while before this can merge.

[woodsp-ibm]

Testing everything with 3.8 works now including logic using Ignis.

[mtreinish]

Cool, if you've manually tested it we can remove the on hold. I've got to update the ignis ci in qiskit-community/qiskit-ignis#298 in to pull in and build aer from source to get the 3.8 job working over there still. But if you've confirmed everything works here it's not like ignis needs a precompiled binary to install since it's all python code

[Jonathanseng]

I am using python 3.8.5 and when try to install: pip install qiskit-aqua[cvx] it shows en error (no match found) anyone had the same problems as me?