Format the specified record as text.
The record's attribute dictionary is used as the operand to a
string formatting operation which yields the returned string.
Before formatting the dictionary, a couple of preparatory steps
are carried out. The message attribute of the record is computed
using LogRecord.getMessage(). If the formatting string uses the
time (as determined by a call to usesTime(), formatTime() is
called to format the event time. If there is exception information,
it is formatted using formatException() and appended to the message.