Add numdays parameter, cleanups

[william-stearns]

• Add --numdays parameter, help text for it, and extend transfer timeout if the user asks for more days than 3. Force to 3 days if user selected 0, 1, or 2 days.
• Adjust the find command to save a list of files to be sent out to a file (instead of storing the output in a variable.) This handles the case where a huge number of files is found and can no longer fit on a command line.
• Modify flock lock file to include the destination and number of days requested. This allows multiple zeek_log_transports to run at the same time - handy when the hourly transfer kicks off while a multiday archive transfer is already running.
• Handle case where source system does not have the "ip" command installed.
• Cosmetic (comment) changes from "bro" to "zeek".
• Add flock command to the required list of tools.
  Satisfies Change zeek_log_transport to handle sending a user-requested number of days of logs #18