libs.mk: allow tests to be sharded
libs.mk: allow tests to be sharded

Creates test_shard.#n [0,9] targets, usable with make -j [jobs]

Change-Id: Ied86dcc89ae72d1690564aa0dd86de10e06d25f9

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