Allow overriding reset operation via project file

Resolve platformio#874

Author: valeros

builder/main.py

@@ -408,8 +408,8 @@ def merge_binaries(source, target, env, for_signature):
             "--chip", mcu,
             "--port", '"$UPLOAD_PORT"',
             "--baud", "$UPLOAD_SPEED",
-            "--before", "default_reset",
-            "--after", "hard_reset",
+            "--before", board.get("upload.before_reset", "default_reset"),
+            "--after", board.get("upload.after_reset", "hard_reset"),
             "write_flash", "-z",
             "--flash_mode", "${__get_board_flash_mode(__env__)}",
             "--flash_freq", "${__get_board_f_flash(__env__)}",