Host is counted twice if it has multiple host tags in Prometheus exporter

[ustcweizhou]

Description

If hosts have multiple host tags, the total/up/down hosts in prometheus exporter are not correct.

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)
• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Enhancement (improves an existing feature and functionality)
• Cleanup (Code refactoring and cleanup, that may add test cases)

Screenshots (if appropriate):

How Has This Been Tested?

[DaanHoogland]

@blueorangutan package

[blueorangutan]

@DaanHoogland a Jenkins job has been kicked to build packages. I'll keep you posted as I make progress.

[blueorangutan]

Packaging result: ✖centos7 ✖centos8 ✖debian. JID-2132

[blueorangutan]

Packaging result: ✖centos7 ✖centos8 ✖debian. JID-2138

[blueorangutan]

Packaging result: ✖centos7 ✖centos8 ✖debian. JID-2139

[Pearl1594]

@ustcweizhou @DaanHoogland
Seems like the build failure is because it is unable to resolve HostVO and hostDao isn't injected

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:compile (default-compile) on project cloud-plugin-integrations-prometheus-exporter: Compilation failure: Compilation failure: 
[ERROR] /jenkins/workspace/acs-pr-centos7-pkg-builder/dist/rpmbuild/BUILD/cloudstack-4.14.1.0-SNAPSHOT/plugins/integrations/prometheus/src/main/java/org/apache/cloudstack/metrics/PrometheusExporterImpl.java:[103,33] error: cannot find symbol
[ERROR]   symbol:   variable hostDao
[ERROR]   location: class PrometheusExporterImpl
[ERROR] /jenkins/workspace/acs-pr-centos7-pkg-builder/dist/rpmbuild/BUILD/cloudstack-4.14.1.0-SNAPSHOT/plugins/integrations/prometheus/src/main/java/org/apache/cloudstack/metrics/PrometheusExporterImpl.java:[103,19] error: cannot find symbol
[ERROR]   symbol:   class HostVO
[ERROR]   location: class PrometheusExporterImpl
[ERROR] -> [Help 1]

[GabrielBrascher]

@blueorangutan package

[blueorangutan]

@GabrielBrascher a Jenkins job has been kicked to build packages. I'll keep you posted as I make progress.

[blueorangutan]

Packaging result: ✔centos7 ✖centos8 ✔debian. JID-2141

[blueorangutan]

Packaging result: ✔centos7 ✖centos8 ✔debian. JID-2147

[yadvr]

LGTM, changes are strictly in promethus plugin; merging based on lgtms and travis tests.