Integration Test - Read the GCP configurations automatically

Various GCP configurations are current required to be exported to the environment;
```
GOOGLE_PROJECT_ID
GOOGLE_REGION
GOOGLE_ZONE
```

This is cumbersome for dev as it is hard to execute test in terminal vs IDE; and needing find variable key-values, make sure spelling is correct etc.

It can be simplified by reading from the configurations set in laptop, or if configuration is net set print a message asking to set configuration with telling quick command and appropriate doc link.

See
* https://github.com/jenkinsci/google-compute-engine-plugin/pull/495#discussion_r1895830873
* https://github.com/jenkinsci/google-compute-engine-plugin/pull/495#discussion_r1895805539