Optional verbose logging for filestoreIntegrity.py

[jantman]

The filestoreIntegrity.py script as currently written doesn't produce any output at all unless it finds a problem with an artifact. When running it against an Artifactory instance with 24 local repositories and over 275,000 artifacts, it just hangs silently at the command line with no indication that it's doing anything at all.

This PR adds a logger to the script and debug-level log messages for each repository and artifact that the script checks. This logging is not present by default, but is enabled by the -v or --verbose arguments.

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[jantman]

Does the comment from the CLA bot indicate that, after two years, someone might finally take a look at this rather trivial change?