Change the alternative rebar detection to avoid messages
Change the alternative rebar detection to avoid messages

The use of 'make -n' introduced some unwanted messages. This
new solution doesn't have this problem.

crownedgrouse/erlang.mk,yannayl/erlang.mk,jj1bdx/erlang.mk,rabbitmq/erlang.mk,hairyhum/erlang.mk,bsmr-erlang/erlang.mk,efcasado/erlang.mk,a12n/erlang.mk,KrzysiekJ/erlang.mk,ingwinlu/erlang.mk,michaelnisi/erlang.mk,nevar/erlang.mk,ninenines/erlang.mk