DBG_LOG_FILE_NAME should be a preference

[sscargal]

When we set a non-zero DBG_LOG_LEVEL, there is no user feedback to show where the debug.log file is being written. The default location is `/var/log/ipmctl/debug.log' in Linux.

We should:

1. Allow the user to get/set the log file location using ipmctl show -preferences and ipmctl set -preferences DBG_LOG_LEVEL=/path/to/my/debug.log
2. Provide a message to the user of the log file location when setting DBG_LOG_LEVEL
3. Document the default log file locations for Linux and Windows in the ipmctl-show-preferences(1) man page within a new DBG_LOG_FILE_NAME section.

For 1, the output would look like this:

# ipmctl show -preferences

CLI_DEFAULT_DIMM_ID=HANDLE
CLI_DEFAULT_SIZE=GiB
APPDIRECT_SETTINGS=RECOMMENDED
APPDIRECT_GRANULARITY=RECOMMENDED
PERFORMANCE_MONITOR_ENABLED=0
PERFORMANCE_MONITOR_INTERVAL_MINUTES=60
EVENT_MONITOR_ENABLED=0
EVENT_MONITOR_INTERVAL_MINUTES=60
EVENT_LOG_MAX=0
DBG_LOG_MAX=0
DBG_LOG_LEVEL=0 
DBG_LOG_FILE_NAME=/var/log/ipmctl/debug.log   <<<<<

For 2, the output to the terminal would look like this:

# ipmctl set -preferences DBG_LOG_LEVEL=4
Set DBG_LOG_LEVEL=4: Success
DBG_LOG_FILE_NAME=/var/log/ipmctl/debug.log

For 3, we could add this to the man page

--- 8< ---
DBG_LOG_LEVEL
    Whether debug logging is enabled in the DCPMM host software. These logs pertain to the operation of the command-line tool only and do not reflect any logging functionality of the DCPMM. One of:

    0: Logging is disabled. This is the default.
    1: Log Errors.
    2: Log Warnings, Errors.
    3: Log Informational, Warnings, Errors.
    4: Log Verbose, Informational, Warnings, Errors.

DBG_LOG_FILE_NAME
    Defines the path to the debug.log file.  The path and filename can be modified using the 'set -preferences' command.  Default locations are:

    Linux: /var/log/ipmctl/debug.log
    Windows: ???

[sscargal]

We could/should do the same with EVENT_LOG_FILE_NAME

[gldiviney]

Thanks - Will review