Fixed an issue when configuration file options partly ignored when `--project-conf` // Resolve #3034 (#3055)

* Fixed an issue when configuration file options partly ignored when using custom ``--project-conf`` // Resolve #3034

* Py2 compatible makedirs

* Fix circle dependency

* Fix broken import in test examples

* Fix history

* Remove YAPF markers

* PyLint fix

* Fix invalid project conf path

* Move PIO Core to the root on Windows, issue with long CPPPATHs

* Respect global PLATFORMIO_BUILD_CACHE_DIR env var

* Fix Appveyor paths

* Minor changes

platformio/run/processor.py

@@ -48,9 +48,11 @@ class EnvironmentProcessor(object):
         return variables
 
     def get_build_targets(self):
-        if self.targets:
-            return [t for t in self.targets]
-        return self.config.get("env:" + self.name, "targets", [])
+        return (
+            self.targets
+            if self.targets
+            else self.config.get("env:" + self.name, "targets", [])
+        )
 
     def process(self):
         if "platform" not in self.options: