Improved changelog entry, also changed error message for HTTParty error

changelogs/unreleased/prometheus-integration-test-setting-fix.yml

 ---
-title: Added rescue block for the test method
+title: Prevent 500 errors caused by testing the Prometheus service
 merge_request: 10994
 author:

lib/gitlab/prometheus.rb

@@ -55,7 +55,7 @@ module Gitlab
     rescue OpenSSL::SSL::SSLError
       raise PrometheusError, "#{url} contains invalid SSL data"
     rescue HTTParty::Error
-      raise PrometheusError, "An error has ocurred"
+      raise PrometheusError, "Network connection error"
     end
 
     def handle_response(response)

spec/lib/gitlab/prometheus_spec.rb

@@ -73,7 +73,7 @@ describe Gitlab::Prometheus, lib: true do
         req_stub = stub_prometheus_request_with_exception(prometheus_url, HTTParty::Error)
 
         expect { subject.send(:get, prometheus_url) }
-          .to raise_error(Gitlab::PrometheusError, "An error has ocurred")
+          .to raise_error(Gitlab::PrometheusError, "Network connection error")
         expect(req_stub).to have_been_requested
       end
     end