nvme-cli: add generic logging functionality

nvme-cli: add generic logging functionality

Add a msg() macro that allows more flexible customization of logging
both at build time and at run time. Allow several log levels, using
the well-known standard sylog levels. Also optionally allow printing
of log timestamps.

Put '#define LOG_FUNCNAME' before '#include "util/log.h"' to enable printing
the name of the calling function before the log message.

Use this functionality in the fabrics code for now, wherever fprintf(stderr, ...)
had been used.

No functional change except changing the output channel of 554db7d ("print
device name when creating a persistent device") from stdout to stderr.

Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>