build.py: Add support for log and run filename changes

build.py: Add support for log and run filename changes

The format of the log file and run file are now selectable
using BB_LOGFMT and BB_RUNFMT, respectively.

The following values may be used:

{task} - task name
{taskfunc} - task.func or func, if task==func
{func} - function name, only available in BB_RUNFMT
{pid} - pid

The log/run files may be placed into a subdirectory that
is relative to T.

Default BB_LOGFMT is: log.{task}.{pid}
Default BB_RUNFMT is: run.{func}.{pid}

(Bitbake rev: 588da606eb81c52cb92d29041e1c67897427bfdf)

Signed-off-by: Mark Hatle <mark.hatle@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>