Implement "require_upload_port" option to "upload" section per board

[ivankravets]

• Add require_upload_port option to boards which require $UPLOAD_PORT for uploading process (avrdude and etc).
• Check require_upload_port in def BeforeUpload(target, source, env):

For example,

    "uno": {
        "build": {
            "core": "arduino",
            "extra_flags": "-DARDUINO_ARCH_AVR -DARDUINO_AVR_UNO",
            "f_cpu": "16000000L",
            "mcu": "atmega328p",
            "variant": "standard"
        },
        "framework": "arduino",
        "name": "Arduino Uno",
        "platform": "atmelavr",
        "upload": {
            "maximum_ram_size": 2048,
            "maximum_size": 32256,
            "protocol": "arduino",
            "require_upload_port" : true,
            "speed": 115200
        }
    },

WARNING! require_upload_port option should have all boards which use avrdude, but don't use usbtiny protocol. raspduino board also requires require_upload_port.

[ivankravets]

This bug blocks #106