Clean up exception handling

[basil]

Various changes to clean up exception handling:

• Stop printing a warning about a missing -master argument when invoking the client with -help
• Print a more friendly message when an invalid command-line argument is specified.
• Catch more specific exceptions where possible.
• Use multi-catch where possible.
• Avoid both logging and re-throwing exceptions. Simpler and more readable to just re-throw and log once from the catch block.
• Consistently throw RetryException from any failures in SwarmClient.
• Always set the cause of the exception whenever rethrowing.
• Remove redundant throws exceptions