waf: ardupilotwaf: add program_dir option to ap_program()

That way we don't force other programs to be built on a directory of their
program group name. The directory name defaults to the program group.

We are separating those two concepts because of the upcoming support for
multiple groups for a program.

Tools/ardupilotwaf/ardupilotwaf.py

@@ -85,7 +85,9 @@ def ap_common_vehicle_libraries(bld):
 _grouped_programs = {}
 
 @conf
-def ap_program(bld, program_group='bin',
+def ap_program(bld,
+               program_group='bin',
+               program_dir=None,
                use_legacy_defines=True,
                program_name=None,
                **kw):
@@ -104,7 +106,10 @@ def ap_program(bld, program_group='bin',
 
     kw['features'] = kw.get('features', []) + bld.env.AP_PROGRAM_FEATURES
 
-    name = os.path.join(program_group, program_name)
+    if not program_dir:
+        program_dir = program_group
+
+    name = os.path.join(program_dir, program_name)
 
     tg_constructor = bld.program
     if bld.env.AP_PROGRAM_AS_STLIB:
@@ -118,7 +123,7 @@ def ap_program(bld, program_group='bin',
         target='#%s' % name,
         name=name,
         program_name=program_name,
-        program_group=program_group,
+        program_dir=program_dir,
         **kw
     )
     _grouped_programs.setdefault(program_group, []).append(tg)

Tools/ardupilotwaf/px4.py

@@ -168,7 +168,7 @@ def px4_firmware(self):
     _update_firmware_sig(fw_task, firmware)
 
     fw_dest = self.bld.bldnode.make_node(
-        os.path.join(self.program_group, '%s.px4' % self.program_name)
+        os.path.join(self.program_dir, '%s.px4' % self.program_name)
     )
     git_hashes = self.create_task('px4_add_git_hashes', firmware, fw_dest)
     git_hashes.set_run_after(fw_task)