toasterui: Create per-build logs

toasterui: Create per-build logs

Rather than relying on bug 8411, which is conveniently creating
separate log files for each of our builds, create our own
log file for each build.

The log files are created in the same tmp directories that
bitbake users, but are timestamped to the millisecond to avoid
name collisions.

Each log file is opened on a ParseStarted event (for builds
triggered by Toaster) or BuildStarted event (for builds on the
command line: Toaster doesn't get the ParseStarted event
for command-line builds).

The log file is closed on the BuildCompleted event, or if the
build fails.

Because we start logging on ParseStarted for Toaster builds,
we're able to capture the "Build Configuration" section which
bitbake writes to output.

[YOCTO #8373]

Signed-off-by: Elliot Smith <elliot.smith@intel.com>
Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>