Fix the host_reachable metric

Without the 'bool' operator qualifier, it would only generate
values for reachable hosts, invalidating the alert logic.
2 jobs for master in 10 minutes and 45 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Docker Build
passed #19761
docker_build_and_release_tests

00:01:08

 
  Test
failed #19762
ai3
run_full_test

00:09:37

 
Name Stage Failure
failed
run_full_test Test
Dump Ansible configuration for test ------------------------------------- 0.29s
ERROR: Command '['ansible-playbook', '-i', 'config.yml', '/builds/ai3/float/test/integration-test-docker.yml']' returned non-zero exit status 2.
Running playbook /builds/ai3/float/test/integration-test-docker.yml...
ERROR: failed to run the integration tests
/builds/ai3/float/test/test-full /builds/ai3/float/test/test-full /builds/ai3/float/test
==> host2: Removing domain...
==> host1: Removing domain...
/builds/ai3/float/test/test-full /builds/ai3/float/test
ERROR: Job failed: exit code 1