autotools.bbclass: When configure fails, dump the config.log files the logs

autotools.bbclass: When configure fails, dump the config.log files the logs

When configure fails, it usually says "see config.log" yet nobody ever shares
the config.log file meaning the person trying to help invariably has to ask
for more information.

This patch dumps all the config.log files into the main bitbake log files when
configure fails, meaning all the information is present to help someone debug
such failures. It does make the log rather larger but this is preferable to
not having enough information in most cases.

[YOCTO #2463]

(From OE-Core rev: 7ad08f5b73aa949a877adc5641b4bb1d007de750)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>