This supports stestr unit tests as well linting with pep8 / flake8

This uses pbr for setup.py which automatically extracts features
and entrypoints out of setup.cfg otherwise you would have to type
this by hand.

Some fields of setup.cfg still need changing the have been
commented out in the meantime.

L2SS-260: Update SDP CPs and MPs to math the XLTR

Closes L2SS-260

See merge request !62

L2SS-244: Expose the SSTs in MPs

Closes L2SS-244

See merge request !56

This has been sync'ed with SDP XLTR version 2021-05-03T09.15.23_sdptr.

L2SS-281: Move attribute extender bug fixes to a dedicated master branch

Closes L2SS-281

See merge request !61

L2SS-244: Return a scalar if given a scalar

(cherry picked from commit 68b98aa8)

L2SS-244: Dim (1,0) is by definition a scalar according to PyTango. Honour this.

(cherry picked from commit d487f383)

L2SS-244: Configure logging to actually see log lines in 'docker logs device-xyz'

(cherry picked from commit 2892211f)

L2SS-244: Default to scalar attributes in attribute_wrapper

(cherry picked from commit ecf4c781)

L2SS-279: Fix the broken image execution

Closes L2SS-279

See merge request !60

L2SS-263:  Fix for broken the image build

Closes L2SS-263

See merge request !57

L2SS-244: Cannot just link to the client in the class! needs to be looked up during device initialisation!

L2SS-244: Rewrite of StatisticsPacket class: unpack everything in 1 go for efficiency, and split off specialistic SST/XST/BST classes