test(all): switch to test package stretchr testify

[gen2thomas]

Solved issues and/or description of the change

#960

• replace gobottest.assert wit assert.Equal by regexp
• replace gobottest.refute wit assert.NotEqual by regexp
• make all tests work
• remove package gobottest

Checklist

• The PR's target branch is 'hybridgroup:dev'
• New and existing unit tests pass locally with my changes (e.g. by run make test)
• No linter errors exist locally (e.g. by run make fmt_check)
• I have performed a self-review of my own code for:
  • no productive code is changed
  • no assertion was accidentally removed