[RealJenkinsRule] Switching hardcoded IPv4 address to loopback address

[PereBueno]

As described in #711.

This change removes the hardcoded 127.0.0.1 address used in RealJenkinsRule and replaces it with the real loopback address, so it will use the IPv4 loopback address, 127.0.0.1, or the IPv6 loopback address, ::1 (in long format, so 0:0:0:0:0:0:0:1).

Regardless address can be overriden via withHttpListenAddress it makes sense to have default address use the right protocol so that method is used only for specific cases.

This change won't affect any test using getUrl() method, as that method returns an URL pointing to localhost so should be version-agnostic.

Testing done

Check running tests using snapshot:
With IPv6

mvn clean test -Djava.net.preferIPv6Addresses=true -Dtest=[......]
...
JENKINS_HOME=[..] SUREFIRE_FORK_NUMBER=1 java -DRealJenkinsRule.location=file:[PATH]/.m2/repository/org/jenkins-ci/main/jenkins-test-harness/999999-SNAPSHOT/jenkins-test-harness-999999-SNAPSHOT.jar [...] --httpPort=0 --httpListenAddress=0:0:0:0:0:0:0:1 --prefix=/jenkins

With IPv4

mvn clean test -Djava.net.preferIPv6Addresses=false -Dtest=[......]
...
JENKINS_HOME=[..] SUREFIRE_FORK_NUMBER=1 java -DRealJenkinsRule.location=file:[PATH]/.m2/repository/org/jenkins-ci/main/jenkins-test-harness/999999-SNAPSHOT/jenkins-test-harness-999999-SNAPSHOT.jar [...] --httpPort=0 --httpListenAddress=127.0.0.1 --prefix=/jenkins

Submitter checklist

Edit tasklist title

Beta Give feedback Tasklist Submitter checklist, more options

• Rename
• Copy markdown
• Delete tasklist

Delete tasklist

Delete tasklist block?

Are you sure? All relationships in this tasklist will be removed.

Cancel Delete

1. Make sure you are opening from a **topic/feature/bugfix branch** (right side) and not your main branch!

   Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
   Options

   • Convert to issue
   • Toggle completion
   • Rename
   • Remove
2. Ensure that the pull request title represents the desired changelog entry

   Ensure that the pull request title represents the desired changelog entry
   Options

   • Convert to issue
   • Toggle completion
   • Rename
   • Remove
3. Please describe what you did

   Please describe what you did
   Options

   • Convert to issue
   • Toggle completion
   • Rename
   • Remove
4. Link to relevant issues in GitHub or Jira

   Link to relevant issues in GitHub or Jira
   Options

   • Convert to issue
   • Toggle completion
   • Rename
   • Remove
5. Link to relevant pull requests, esp. upstream and downstream changes

   Link to relevant pull requests, esp. upstream and downstream changes
   Options

   • Convert to issue
   • Toggle completion
   • Rename
   • Remove
6. Ensure you have provided tests - that demonstrates feature works or fixes the issue

   Ensure you have provided tests - that demonstrates feature works or fixes the issue
   Options

   • Convert to issue
   • Toggle completion
   • Rename
   • Remove

Add item to Submitter checklist