Makefile: check for 'replay' env variable and change build dir accordingly
Makefile: check for 'replay' env variable and change build dir accordingly

For replay with the new logger, we want a separate build dir so that the
parameters file and orb rules don't get mixed up.

jlecoeur/Firmware,mje-nz/PX4-Firmware,jlecoeur/Firmware,Aerotenna/Firmware,mcgill-robotics/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,dagar/Firmware,jlecoeur/Firmware,mcgill-robotics/Firmware,PX4/Firmware,Aerotenna/Firmware,mcgill-robotics/Firmware,darknight-007/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,darknight-007/Firmware,Aerotenna/Firmware,krbeverx/Firmware,darknight-007/Firmware,mcgill-robotics/Firmware,Aerotenna/Firmware,acfloria/Firmware,darknight-007/Firmware,dagar/Firmware,Aerotenna/Firmware,PX4/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,PX4/Firmware,jlecoeur/Firmware,Aerotenna/Firmware,jlecoeur/Firmware,krbeverx/Firmware,Aerotenna/Firmware,dagar/Firmware,dagar/Firmware,krbeverx/Firmware,PX4/Firmware,acfloria/Firmware,PX4/Firmware,jlecoeur/Firmware,acfloria/Firmware,mcgill-robotics/Firmware,dagar/Firmware,krbeverx/Firmware,dagar/Firmware,mcgill-robotics/Firmware,jlecoeur/Firmware,acfloria/Firmware,mcgill-robotics/Firmware,mje-nz/PX4-Firmware,darknight-007/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,jlecoeur/Firmware,PX4/Firmware,krbeverx/Firmware