Merge branch 'sh-show-database-connection-errors' into 'master'

Log database errors

Closes #72

See merge request gitlab-org/gitlab-exporter!121
2 jobs for master in 53 seconds
Status Job ID Name Coverage
  Test
passed #8199891
gitlab-org
rspec

00:00:50

passed #8199892
gitlab-org
rubocop

00:00:53