ci: fix tests

- flask docu on readthedocs is no longer available
- use beta tags for autoscale runners
8 jobs for master in 14 minutes and 59 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Test
passed py3.5-min-mysql #16558
beta

00:11:24

92.0%
passed py3.5-min-postgresql #16556
beta

00:09:50

92.0%
passed py3.5-min-sqlite #16554
beta

00:09:55

91.0%
passed py3.5-pypi-mysql #16559
beta

00:11:02

92.0%
passed py3.5-pypi-postgresql #16557
beta

00:10:11

92.0%
passed py3.5-pypi-sqlite #16555
beta

00:11:07

91.0%
 
  Deploy
passed pages #16560

00:03:33

passed pages:deploy

00:00:02