Update to the latest version of buildbot configuration script

[tyu011]

Main changes:

• Build optimised version of OpenCMISS-Iron on buildbot
• Hide some unimportant buildsteps
• Add a build step to clean build logs that are more than 30 days old.

[adamreeve]

Hi Ting, this looks good. Just a couple of comments as above.

Cheers,

Adam