Make test_sky work on machines with fewer than 4 CPUs. Exclude the 'conf' subdirectory from being scanned for tests, since it's for support files. Drop all the unused extensions from _supported_file_extensions.
Make test_sky work on machines with fewer than 4 CPUs.
Exclude the 'conf' subdirectory from being scanned for tests, since it's for support files.
Drop all the unused extensions from _supported_file_extensions.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/679303002

xunmengfeng/engine,afandria/sky_engine,mdakin/engine,mikejurka/engine,takaaptech/sky_engine,aam/engine,devoncarew/engine,chinmaygarde/sky_engine,mxia/engine,chinmaygarde/sky_engine,cdotstout/sky_engine,xunmengfeng/engine,flutter/engine,zhangxq5012/sky_engine,cdotstout/sky_engine,abarth/sky_engine,jimsimon/sky_engine,chinmaygarde/flutter_engine,chinmaygarde/sky_engine,mpcomplete/engine,flutter/engine,afandria/sky_engine,tvolkert/engine,flutter/engine,krisgiesing/sky_engine,jimsimon/sky_engine,aam/engine,afandria/sky_engine,lyceel/engine,jimsimon/sky_engine,zhangxq5012/sky_engine,aam/engine,qiankunshe/sky_engine,Hixie/sky_engine,afandria/sky_engine,flutter/engine,mdakin/engine,afandria/sky_engine,iansf/sky_engine,jason-simmons/flutter_engine,jamesr/flutter_engine,mpcomplete/engine,jamesr/flutter_engine,flutter/engine,krisgiesing/sky_engine,takaaptech/sky_engine,qiankunshe/sky_engine,jamesr/flutter_engine,jamesr/flutter_engine,TribeMedia/sky_engine,takaaptech/sky_engine,jamesr/sky_engine,aam/engine,takaaptech/sky_engine,afandria/sky_engine,TribeMedia/sky_engine,mxia/engine,Hixie/sky_engine,mikejurka/engine,mpcomplete/flutter_engine,chinmaygarde/flutter_engine,Hixie/sky_engine,jason-simmons/flutter_engine,mikejurka/engine,iansf/sky_engine,lyceel/engine,lyceel/engine,jason-simmons/sky_engine,xunmengfeng/engine,cdotstout/sky_engine,jamesr/sky_engine,chinmaygarde/sky_engine,takaaptech/sky_engine,mxia/engine,abarth/sky_engine,jimsimon/sky_engine,mxia/engine,krisgiesing/sky_engine,lyceel/engine,qiankunshe/sky_engine,rmacnak-google/engine,chinmaygarde/flutter_engine,jason-simmons/sky_engine,abarth/sky_engine,rmacnak-google/engine,rmacnak-google/engine,mpcomplete/flutter_engine,jason-simmons/sky_engine,chinmaygarde/flutter_engine,jason-simmons/sky_engine,chinmaygarde/sky_engine,tvolkert/engine,axinging/sky_engine,TribeMedia/sky_engine,krisgiesing/sky_engine,mdakin/engine,tvolkert/engine,jamesr/flutter_engine,takaaptech/sky_engine,mxia/engine,chinmaygarde/flutter_engine,jamesr/sky_engine,jason-simmons/sky_engine,axinging/sky_engine,Hixie/sky_engine,takaaptech/sky_engine,flutter/engine,rmacnak-google/engine,mikejurka/engine,mdakin/engine,jason-simmons/flutter_engine,jamesr/flutter_engine,TribeMedia/sky_engine,axinging/sky_engine,iansf/sky_engine,mpcomplete/engine,mdakin/engine,mdakin/engine,jamesr/flutter_engine,devoncarew/sky_engine,mpcomplete/flutter_engine,abarth/sky_engine,xunmengfeng/engine,krisgiesing/sky_engine,zhangxq5012/sky_engine,mdakin/engine,xunmengfeng/engine,jamesr/sky_engine,Hixie/sky_engine,cdotstout/sky_engine,mikejurka/engine,rmacnak-google/engine,mpcomplete/flutter_engine,cdotstout/sky_engine,cdotstout/sky_engine,devoncarew/engine,devoncarew/sky_engine,tvolkert/engine,zhangxq5012/sky_engine,jamesr/flutter_engine,devoncarew/sky_engine,aam/engine,tvolkert/engine,devoncarew/sky_engine,jason-simmons/sky_engine,jimsimon/sky_engine,mpcomplete/flutter_engine,tvolkert/engine,jason-simmons/sky_engine,devoncarew/engine,qiankunshe/sky_engine,mpcomplete/engine,cdotstout/sky_engine,abarth/sky_engine,devoncarew/engine,qiankunshe/sky_engine,jason-simmons/flutter_engine,devoncarew/engine,TribeMedia/sky_engine,takaaptech/sky_engine,jamesr/sky_engine,devoncarew/sky_engine,mpcomplete/engine,jason-simmons/flutter_engine,mxia/engine,rmacnak-google/engine,TribeMedia/sky_engine,lyceel/engine,mpcomplete/engine,tvolkert/engine,xunmengfeng/engine,mikejurka/engine,jimsimon/sky_engine,jimsimon/sky_engine,jimsimon/sky_engine,zhangxq5012/sky_engine,qiankunshe/sky_engine,jason-simmons/flutter_engine,axinging/sky_engine,mikejurka/engine,abarth/sky_engine,lyceel/engine,chinmaygarde/sky_engine,qiankunshe/sky_engine,TribeMedia/sky_engine,mikejurka/engine,zhangxq5012/sky_engine,iansf/sky_engine,abarth/sky_engine,qiankunshe/sky_engine,flutter/engine,jamesr/sky_engine,axinging/sky_engine,xunmengfeng/engine,krisgiesing/sky_engine,TribeMedia/sky_engine,Hixie/sky_engine,aam/engine,axinging/sky_engine,devoncarew/engine,zhangxq5012/sky_engine,zhangxq5012/sky_engine,mikejurka/engine,jamesr/flutter_engine,axinging/sky_engine,chinmaygarde/sky_engine,krisgiesing/sky_engine,mxia/engine,jason-simmons/flutter_engine,jason-simmons/flutter_engine,chinmaygarde/flutter_engine,afandria/sky_engine,iansf/sky_engine,devoncarew/sky_engine,takaaptech/sky_engine,Hixie/sky_engine,flutter/engine,mdakin/engine,Hixie/sky_engine,devoncarew/engine,iansf/sky_engine,aam/engine,mxia/engine,TribeMedia/sky_engine,chinmaygarde/flutter_engine,mpcomplete/engine,devoncarew/sky_engine,iansf/sky_engine,jimsimon/sky_engine,rmacnak-google/engine,axinging/sky_engine,iansf/sky_engine,mpcomplete/engine,mpcomplete/flutter_engine,lyceel/engine,jamesr/sky_engine,axinging/sky_engine,afandria/sky_engine,aam/engine,zhangxq5012/sky_engine