all_builds.py: support for sharding builds
all_builds.py: support for sharding builds

Allow sharding of the builds with the --shard= and --shards= options.

Change-Id: I9d5552ad2edc0b1210e96f0e94ce7dfd645c45f8

luctrudeau/aom,liqianggao/libvpx,jdm/libvpx,mwgoldsmith/libvpx,goodleixiao/vpx,lyx2014/libvpx_c,shyamalschandra/libvpx,WebRTC-Labs/libvpx,shareefalis/libvpx,mbebenita/aom,gshORTON/webm.libvpx,kim42083/webm.libvpx,felipebetancur/libvpx,running770/libvpx,ittiamvpx/libvpx,kleopatra999/webm.libvpx,Maria1099/webm.libvpx,mwgoldsmith/libvpx,gshORTON/webm.libvpx,smarter/aom,WebRTC-Labs/libvpx,goodleixiao/vpx,matanbs/vp982,Topopiccione/libvpx,kleopatra999/webm.libvpx,mwgoldsmith/vpx,shareefalis/libvpx,n4t/libvpx,Laknot/libvpx,Distrotech/libvpx,pcwalton/libvpx,Maria1099/webm.libvpx,shyamalschandra/libvpx,altogother/webm.libvpx,luctrudeau/aom,thdav/aom,matanbs/webm.libvpx,lyx2014/libvpx_c,pcwalton/libvpx,hsueceumd/test_hui,openpeer/libvpx_new,mbebenita/aom,shyamalschandra/libvpx,WebRTC-Labs/libvpx,hsueceumd/test_hui,zofuthan/libvpx,liqianggao/libvpx,sanyaade-teachings/libvpx,charup/https---github.com-webmproject-libvpx-,jmvalin/aom,shacklettbp/aom,sanyaade-teachings/libvpx,turbulenz/libvpx,shyamalschandra/libvpx,mbebenita/aom,running770/libvpx,mwgoldsmith/libvpx,cinema6/libvpx,shyamalschandra/libvpx,VTCSecureLLC/libvpx,cinema6/libvpx,smarter/aom,matanbs/webm.libvpx,charup/https---github.com-webmproject-libvpx-,matanbs/webm.libvpx,openpeer/libvpx_new,webmproject/libvpx,n4t/libvpx,turbulenz/libvpx,vasilvv/esvp8,turbulenz/libvpx,ittiamvpx/libvpx,turbulenz/libvpx,jdm/libvpx,VTCSecureLLC/libvpx,Laknot/libvpx,Laknot/libvpx,smarter/aom,openpeer/libvpx_new,cinema6/libvpx,n4t/libvpx,matanbs/vp982,felipebetancur/libvpx,sanyaade-teachings/libvpx,iniwf/webm.libvpx,jmvalin/aom,ShiftMediaProject/libvpx,Maria1099/webm.libvpx,ShiftMediaProject/libvpx,pcwalton/libvpx,liqianggao/libvpx,jacklicn/webm.libvpx,luctrudeau/aom,liqianggao/libvpx,GrokImageCompression/aom,reimaginemedia/webm.libvpx,luctrudeau/aom,iniwf/webm.libvpx,goodleixiao/vpx,running770/libvpx,webmproject/libvpx,vasilvv/esvp8,zofuthan/libvpx,stewnorriss/libvpx,matanbs/vp982,shacklettbp/aom,felipebetancur/libvpx,Laknot/libvpx,smarter/aom,iniwf/webm.libvpx,stewnorriss/libvpx,vasilvv/esvp8,jdm/libvpx,webmproject/libvpx,pcwalton/libvpx,vasilvv/esvp8,Distrotech/libvpx,altogother/webm.libvpx,turbulenz/libvpx,mwgoldsmith/libvpx,shareefalis/libvpx,Maria1099/webm.libvpx,abwiz0086/webm.libvpx,matanbs/webm.libvpx,kim42083/webm.libvpx,pcwalton/libvpx,ittiamvpx/libvpx-1,goodleixiao/vpx,webmproject/libvpx,Acidburn0zzz/webm.libvpx,vasilvv/esvp8,n4t/libvpx,Suvarna1488/webm.libvpx,Suvarna1488/webm.libvpx,felipebetancur/libvpx,kim42083/webm.libvpx,Maria1099/webm.libvpx,ittiamvpx/libvpx-1,Suvarna1488/webm.libvpx,GrokImageCompression/aom,Distrotech/libvpx,turbulenz/libvpx,vasilvv/esvp8,charup/https---github.com-webmproject-libvpx-,shacklettbp/aom,kim42083/webm.libvpx,jacklicn/webm.libvpx,felipebetancur/libvpx,altogother/webm.libvpx,altogother/webm.libvpx,goodleixiao/vpx,zofuthan/libvpx,kleopatra999/webm.libvpx,Suvarna1488/webm.libvpx,Distrotech/libvpx,running770/libvpx,mwgoldsmith/libvpx,Acidburn0zzz/webm.libvpx,shacklettbp/aom,mwgoldsmith/vpx,ittiamvpx/libvpx,jmvalin/aom,GrokImageCompression/aom,stewnorriss/libvpx,shyamalschandra/libvpx,jacklicn/webm.libvpx,smarter/aom,goodleixiao/vpx,mbebenita/aom,Suvarna1488/webm.libvpx,liqianggao/libvpx,ShiftMediaProject/libvpx,kleopatra999/webm.libvpx,shareefalis/libvpx,kalli123/webm.libvpx,webmproject/libvpx,reimaginemedia/webm.libvpx,ittiamvpx/libvpx-1,cinema6/libvpx,kalli123/webm.libvpx,turbulenz/libvpx,shareefalis/libvpx,Suvarna1488/webm.libvpx,Topopiccione/libvpx,smarter/aom,n4t/libvpx,felipebetancur/libvpx,jmvalin/aom,pcwalton/libvpx,lyx2014/libvpx_c,lyx2014/libvpx_c,GrokImageCompression/aom,mwgoldsmith/vpx,ittiamvpx/libvpx,jmvalin/aom,Topopiccione/libvpx,luctrudeau/aom,Distrotech/libvpx,cinema6/libvpx,thdav/aom,ittiamvpx/libvpx,running770/libvpx,jacklicn/webm.libvpx,mwgoldsmith/vpx,reimaginemedia/webm.libvpx,reimaginemedia/webm.libvpx,kalli123/webm.libvpx,shacklettbp/aom,cinema6/libvpx,gshORTON/webm.libvpx,mwgoldsmith/vpx,openpeer/libvpx_new,matanbs/vp982,sanyaade-teachings/libvpx,matanbs/webm.libvpx,mbebenita/aom,gshORTON/webm.libvpx,zofuthan/libvpx,mwgoldsmith/libvpx,hsueceumd/test_hui,stewnorriss/libvpx,charup/https---github.com-webmproject-libvpx-,ShiftMediaProject/libvpx,zofuthan/libvpx,altogother/webm.libvpx,Maria1099/webm.libvpx,openpeer/libvpx_new,abwiz0086/webm.libvpx,jdm/libvpx,Topopiccione/libvpx,shacklettbp/aom,VTCSecureLLC/libvpx,lyx2014/libvpx_c,thdav/aom,matanbs/vp982,gshORTON/webm.libvpx,VTCSecureLLC/libvpx,stewnorriss/libvpx,charup/https---github.com-webmproject-libvpx-,matanbs/webm.libvpx,sanyaade-teachings/libvpx,shareefalis/libvpx,WebRTC-Labs/libvpx,jacklicn/webm.libvpx,VTCSecureLLC/libvpx,mbebenita/aom,openpeer/libvpx_new,iniwf/webm.libvpx,luctrudeau/aom,turbulenz/libvpx,kalli123/webm.libvpx,kim42083/webm.libvpx,Acidburn0zzz/webm.libvpx,lyx2014/libvpx_c,iniwf/webm.libvpx,abwiz0086/webm.libvpx,liqianggao/libvpx,Distrotech/libvpx,reimaginemedia/webm.libvpx,kalli123/webm.libvpx,kim42083/webm.libvpx,ShiftMediaProject/libvpx,zofutha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