Add mavftp library and example code that uses it

[amilcarlucas]

Like spoken on the dev call this adds a mavftp library and an example script that uses it to:

• get parameter values
• get default parameter values
• put a lua script file
• get the latest .bin log file

This is the --help of the main mavftp.py application, it supports a similar syntax to the MAVProxy embedded mavftp functionality:

usage: mavftp.py [-h] [--baudrate BAUDRATE] [--device DEVICE] [--source-system SOURCE_SYSTEM] [--loglevel LOGLEVEL] [--debug DEBUG] [--pkt_loss_tx PKT_LOSS_TX]
                 [--pkt_loss_rx PKT_LOSS_RX] [--max_backlog MAX_BACKLOG] [--burst_read_size BURST_READ_SIZE] [--write_size WRITE_SIZE] [--write_qsize WRITE_QSIZE]
                 [--retry_time RETRY_TIME]
                 {get,getparams,put,list,mkdir,rmdir,rm,rename,crc} ...

MAVFTP - MAVLink File Transfer Protocol. A tool to do file operations between a ground control station and a drone using the MAVLink protocol.

positional arguments:
  {get,getparams,put,list,mkdir,rmdir,rm,rename,crc}
    get                 Get a file from the remote flight controller.
    getparams           Get and decode parameters from the remote flight controller.
    put                 Put a file to the remote flight controller.
    list                List files in a directory on the remote flight controller.
    mkdir               Create a directory on the remote flight controller.
    rmdir               Remove a directory on the remote flight controller.
    rm                  Remove a file on the remote flight controller.
    rename              Rename a file or directory on the remote flight controller.
    crc                 Calculate the CRC of a file on the remote flight controller.

optional arguments:
  -h, --help            show this help message and exit
  --baudrate BAUDRATE   master port baud rate. Defaults to 115200
  --device DEVICE       serial device. For windows use COMx where x is the port number. For Unix use /dev/ttyUSBx where x is the port number. Defaults to autodetection
  --source-system SOURCE_SYSTEM
                        MAVLink source system for this GCS. Defaults to 250
  --loglevel LOGLEVEL   log level. Defaults to INFO
  --debug DEBUG         Debug level 0 for none, 2 for max verbosity. Defaults to 0
  --pkt_loss_tx PKT_LOSS_TX
                        Packet loss on TX. Defaults to 0
  --pkt_loss_rx PKT_LOSS_RX
                        Packet loss on RX. Defaults to 0
  --max_backlog MAX_BACKLOG
                        Max backlog. Defaults to 5
  --burst_read_size BURST_READ_SIZE
                        Burst read size. Defaults to 80
  --write_size WRITE_SIZE
                        Write size. Defaults to 80
  --write_qsize WRITE_QSIZE
                        Write queue size. Defaults to 5
  --retry_time RETRY_TIME
                        Retry time. Defaults to 0.5

To test the example do:

python3 -m examples.mavftp_example --loglevel DEBUG

[amilcarlucas]

@tridge I did some small pylint fixes on top of your changes. Thanks.

[amilcarlucas]

I will add a put to upload a .lua script to the example and add code to download the lastest .bin log file.
Once that is done I think this can go in

[amilcarlucas]

@peterbarker looks like there is no pylint running here. Should I add that?

[amilcarlucas]

Please do not squash the two commits

[amilcarlucas]

Tested on CubeBlack. All operations work fine. But sometimes operations after a cmd_get do not work. So I still have some work to do.

[amilcarlucas]

OK, got it to work. It has much improved error handling.

Also added some tests