Improve log message when fetching, starting analyzers

What does this MR do?

Upgrade to common v2.5.6

• Log when downloading, starting analyzers gitlab-org/security-products/analyzers/common!64 (merged)
• Suppress the progress message on pulling analyzer image gitlab-org/security-products/analyzers/common!65 (merged)

See job output:

 2020/01/17 16:32:51 [retire.js] Downloading analyzer...
 ............................................................
 2020/01/17 16:33:02 [retire.js] Starting analyzer...

What are the relevant issue numbers?

gitlab-org/gitlab#196159 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• [-] Documentation created/updated for GitLab EE, if necessary
• [-] Documentation created/updated for this project, if necessary
• [-] Documentation reviewed by technical writer or follow-up review issue created
• [-] Tests added for this feature/bug
  • This has been manually using the QA jobs of the pipeline. For instance, look for Downloading analyzer and Starting analyzer in dependency_scanning job of tests/ruby-bundler.
• [-] Job definition updated, if necessary
• [-] Conforms to the code review guidelines
• [-] Conforms to the Go guidelines
• [-] Security reports checked/validated by reviewer

/cc @tnir