increased version number and forced number of events per thread for the CI

atlas/gen/atlas-gen.spec

 HEPWL_BMKEXE=atlas-gen-bmk.sh
-HEPWL_BMKOPTS="" # -c replaces -n as of v0.11
+HEPWL_BMKOPTS="-e 4" # -c replaces -n as of v0.11
 HEPWL_BMKDIR=atlas-gen
 HEPWL_BMKDESCRIPTION="ATLAS Event Generation based on athena version 19.2.5.5"
 HEPWL_DOCKERIMAGENAME=atlas-gen-bmk
-HEPWL_DOCKERIMAGETAG=v0.15 # versions >= v0.11 use common bmk driver
+HEPWL_DOCKERIMAGETAG=v0.16 # versions >= v0.11 use common bmk driver
 HEPWL_CVMFSREPOS=atlas.cern.ch,atlas-condb.cern.ch,sft.cern.ch
 HEPWL_EXTEND_SFT_SPEC=./sft_spec_custom.txt