Update build.sh

[kalebskeithley]

whatever cleans the workspace where the tree is cloned apparently just does rm -rf * which does not delete .foo, and in particular the .python-shebangs file from previous build in this workspace

[nigelbabu]

I'd like to add this to the code that actually does the clean up rather than here. That's in build-jobs on Gerrit.

[kalebskeithley]

That'd be my preference too. I looked for something like that, but it's too well hidden. So you fixed it there already? (Where ever that is?)

And I can't find anything named build-jobs in gerrit. (I see the build-job task in jenkins.)

I see the cleanup.sh script that cleans most things. Do we really just keep cloning into the same directory without ever doing an rm -rf * (and an rm -rf .*) ?