Add integration tests to detect that the configuration is dumped in the stdout/logfile.

[kislaykishore]

Background:
GCSFuse dumps the configuration that it was started with in the log file/standard output depending upon whether it was started in background/foreground mode. We'd like to add integration tests to verify that the logging does happen.

Motivation:
Configuration logging helps determine what was the configuration of GCSFuse when it was run. It comes in handy while debugging issues.

Acceptance Criteria:
Add an integration test that should test whether the configuration is being dumped into the log file. We don't want to compare exactly whether all the flags are being written to since that'll lead to it becoming a change-detector test; we just want to know whether the dumping is happening.