Merge branch 'sh-optimize-db-probe' into 'master'

Reduce CPU utilization of row count query

Closes #75

See merge request gitlab-org/gitlab-exporter!123
6 jobs for master in 2 minutes and 15 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #9075335
gitlab-org
gemnasium-dependency_scanning

00:00:25

passed #9075336
gitlab-org
license_scanning

00:02:15

passed #9075339
gitlab-org
rspec

00:01:25

passed #9075340
gitlab-org
rubocop

00:01:27

passed #9075338
gitlab-org
secret_detection

00:00:15

passed #9075337
gitlab-org
secret_detection_default_branch

00:00:23