Use RollingFileAppender only when log_limit_in_kbytes greater than 0

[jtduffy]

This corrects the agent logger agent config so that a RollingFileAppender is only created if the setting log_limit_in_kbytes is > 0. Before, if the log_limit_in_kbytes was 0 but log_file_count was > 1, a RollingFileAppender was created, but with a NoOp trigger policy, no rolling ever actually occurred.

Created unit tests for these scenarios.

The docs will be clarified with the follow info:

• if log_daily is true, it will use the file_count value, with a minimum value of 1; if log_limit_in_kbytes > 0, a composite trigger policy will be configured: daily roll and size based roll
• if log_limit_in_kbytes > 0, a rolling file appender strategy will be configured, using the configured log_file_count (minimum of 1)
• Otherwise, no log rolling strategy will be configured

This is a non-breaking change, since any environment with log_limit_in_kbytes == 0 and log_file_limit > 1 will result in a regular, non-rolling file appender, which is equivalent to prior behavior.