Clean build dir if bdist_wheel fails
Clean build dir if bdist_wheel fails

When pip tries to build a wheel but fails, setup.py install is run in
the same directory.  However, some build files are not compatible
between 'install' and 'bdist_wheel', particularly scripts - the shebang
lines are different.  Pip now cleans the build dir after a failed
bdist_wheel so that pip doesn't install broken scripts.

Closes #3006

alex/pip,fiber-space/pip,RonnyPfannschmidt/pip,natefoo/pip,pfmoore/pip,sigmavirus24/pip,alex/pip,sbidoul/pip,willingc/pip,ncoghlan/pip,pypa/pip,pradyunsg/pip,mindw/pip,alex/pip,benesch/pip,willingc/pip,fiber-space/pip,rouge8/pip,xavfernandez/pip,mindw/pip,zvezdan/pip,rbtcollins/pip,pypa/pip,benesch/pip,natefoo/pip,esc/pip,dstufft/pip,zvezdan/pip,James-Firth/pip,techtonik/pip,xavfernandez/pip,esc/pip,pradyunsg/pip,pfmoore/pip,RonnyPfannschmidt/pip,xavfernandez/pip,benesch/pip,techtonik/pip,RonnyPfannschmidt/pip,atdaemon/pip,sigmavirus24/pip,jythontools/pip,rouge8/pip,dstufft/pip,James-Firth/pip,atdaemon/pip,willingc/pip,rouge8/pip,nthall/pip,natefoo/pip,esc/pip,mindw/pip,rbtcollins/pip,fiber-space/pip,dstufft/pip,atdaemon/pip,nthall/pip,ncoghlan/pip,sbidoul/pip,jythontools/pip,zvezdan/pip,ncoghlan/pip,nthall/pip,sigmavirus24/pip,James-Firth/pip,jythontools/pip,techtonik/pip,rbtcollins/pip