Improvements to Daily Benchmarks Script

[jdjaustin]

Issue summary
Implement improvements to benchmarking script:

• Add a "peak" memory benchmark step to /forest/scripts/benchmark_db/bench.rb.
  For example, once a snapshot has been imported and the node synced up to HEAD, let it run for 2 hours and measure how RSS and VSZ are evolving. This should help pinpoint if a regression occurs (i.e., a memory leak is introduced).
• Create common error handler.
• Other improvements/optimizations as needed (e.g., long form command line options, modify private module designations, etc.).
• Check preconditions before running script (enough disk space and ulimit -n is correctly set).
• Delete cloned git repos at the end of script instead of after each client run.
• Investigate and fix issue with missing gems when using bundle install.

Other information and links
Proposed during discussions under issue #2208.

[jdjaustin]

Tasks moved to tracking issue in forest-iac.