makefiles/docker.inc.mk: add PROGRAMMER to the exported variables
makefiles/docker.inc.mk: add PROGRAMMER to the exported variables

Depending on the PROGRAMMER used, the file used for flashing may be
different, like openocd/jlink, so the file being generated when
compiling should be different.

Because of this, when building in docker, the build system needs to know
for which programmer you are building for.

This manifested for 'nordic_softdevice' applications when using 'openocd'
but is not limited to this case.

kYc0o/RIOT,authmillenon/RIOT,yogo1212/RIOT,OTAkeys/RIOT,yogo1212/RIOT,x3ro/RIOT,kaspar030/RIOT,authmillenon/RIOT,rfuentess/RIOT,kaspar030/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,aeneby/RIOT,basilfx/RIOT,OlegHahm/RIOT,basilfx/RIOT,aeneby/RIOT,josephnoir/RIOT,x3ro/RIOT,OTAkeys/RIOT,ant9000/RIOT,yogo1212/RIOT,kaspar030/RIOT,kYc0o/RIOT,jasonatran/RIOT,mtausig/RIOT,toonst/RIOT,basilfx/RIOT,jasonatran/RIOT,OTAkeys/RIOT,toonst/RIOT,ant9000/RIOT,authmillenon/RIOT,cladmi/RIOT,aeneby/RIOT,cladmi/RIOT,miri64/RIOT,authmillenon/RIOT,x3ro/RIOT,jasonatran/RIOT,cladmi/RIOT,basilfx/RIOT,josephnoir/RIOT,ant9000/RIOT,smlng/RIOT,kYc0o/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,ant9000/RIOT,smlng/RIOT,smlng/RIOT,cladmi/RIOT,basilfx/RIOT,toonst/RIOT,jasonatran/RIOT,mtausig/RIOT,miri64/RIOT,aeneby/RIOT,rfuentess/RIOT,smlng/RIOT,toonst/RIOT,kaspar030/RIOT,miri64/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,mtausig/RIOT,cladmi/RIOT,smlng/RIOT,mtausig/RIOT,authmillenon/RIOT,yogo1212/RIOT,miri64/RIOT,rfuentess/RIOT,OTAkeys/RIOT,yogo1212/RIOT,yogo1212/RIOT,mtausig/RIOT,rfuentess/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,ant9000/RIOT,rfuentess/RIOT,josephnoir/RIOT,miri64/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,OlegHahm/RIOT,aeneby/RIOT,x3ro/RIOT,toonst/RIOT,josephnoir/RIOT,RIOT-OS/RIOT,x3ro/RIOT,kaspar030/RIOT,josephnoir/RIOT