toaster: improve logging facilities for toaster

toaster: improve logging facilities for toaster

This patch improves the logging facilities for toaster in order
to help diagnose bugs that happen on user machines.

The logs are stored now under "/tmp/toaster_$$" where $$ is a
PID-based unique identifier. On shutdown, toaster will automatically
erase all logs unless errors are listed in the log file.

On error, Toaster provides suggestions on what to do.

This patch includes a minor fix found as a result of logging
improvements.

Signed-off-by: Alexandru DAMIAN <alexandru.damian@intel.com>