Improve log message when fetching, starting analyzers by bumping common from 2.5.1 to 2.5.6

What does this MR do?

Upgrade from 2.5.1 to common v2.5.6, like one for DS (dependency-scanning!56 (merged)):

• 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)

CI job log is as follow:

[...]
2020/01/25 14:46:20 [bandit] Downloading analyzer...
......................................................................
2020/01/25 14:46:46 [bandit] Starting analyzer...
[...]
2020/01/25 14:46:51 [flawfinder] Downloading analyzer...
.......................
2020/01/25 14:46:51 [flawfinder] Starting analyzer...
[...]
2020/01/25 14:46:52 [secrets] Downloading analyzer...
..........................
2020/01/25 14:46:55 [secrets] Starting analyzer...
[...]
2020/01/25 14:47:02 [spotbugs] Downloading analyzer...
......................................................................
2020/01/25 14:47:42 [spotbugs] Starting analyzer...
[...]

What are the relevant issue numbers?

gitlab-org/gitlab#196159 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• [n/a] Documentation created/updated for GitLab EE, if necessary
• [n/a] Documentation created/updated for this project, if necessary
• [n/a] Documentation reviewed by technical writer or follow-up review issue created
• [n/a] Tests added for this feature/bug
• [n/a] Job definition updated, if necessary
  • [n/a] Job definition example
  • [n/a] CI Templates (to be removed)
  • [n/a] Vendored CI Templates (also in CE)
  • [n/a] Ensure that all of the ENV vars supported are propagated to Docker containers upon docker run in job definitions
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer