global: drop mock dependency and use unittest.mock

Since this module only supports python 3.5+ the mock dependency can
safely be replaced by the Python standard library unittest.mock
13 jobs for 46-create-api-to-get-all-active-background-jobs in 13 minutes and 43 seconds (queued for 5 seconds)
Status Name Job ID Coverage
  Test
passed py3.5-min-mysql #22826

00:08:59

95.0%
passed py3.5-min-postgresql #22824

00:08:56

95.0%
passed py3.5-min-sqlite #22822

00:09:52

94.0%
passed py3.5-pypi-mysql #22827

00:13:43

95.0%
passed py3.5-pypi-postgresql #22834

00:09:06

95.0%
passed py3.5-pypi-sqlite #22823

00:08:54

94.0%
passed py3.6-min-mysql #22832

00:09:13

95.0%
passed py3.6-min-postgresql #22830

00:09:09

95.0%
passed py3.6-min-sqlite #22828

00:09:03

94.0%
passed py3.6-pypi-mysql #22833

00:09:07

95.0%
passed py3.6-pypi-postgresql #22831

00:09:13

95.0%
passed py3.6-pypi-sqlite #22829

00:09:03

94.0%
failed py3.5-pypi-postgresql #22825

00:00:48