waf: allow for "./waf bootloader"

easier build of the bootloader

Tools/AP_Bootloader/wscript

@@ -4,5 +4,5 @@
 def build(bld):
     bld.ap_program(
         use='ap',
-        program_groups='tools',
+        program_groups='bootloader'
     )

wscript

@@ -456,7 +456,7 @@ ardupilotwaf.build_command('check-all',
     doc='shortcut for `waf check --alltests`',
 )
 
-for name in ('antennatracker', 'copter', 'heli', 'plane', 'rover', 'sub'):
+for name in ('antennatracker', 'copter', 'heli', 'plane', 'rover', 'sub', 'bootloader'):
     ardupilotwaf.build_command(name,
         program_group_list=name,
         doc='builds %s programs' % name,