add checktool endpoint and force download

[facchinm]

In this way, the communication between agent and BE will be something like

-> checktool bossac
<- {ToolVersions: ["bossac", "bossac-1.6-arduino]}
-> downloadtool bossac-1.6.1-arduino http://downloads.arduino.cc/....

[facchinm]

@matteosuppo

[matteosuppo]

The first time I download a tool it works fine, but if the tool is already there (maybe because I want to update it) it fails:

downloadtool avrdude https://downloads.arduino.cc/tools
{"DownloadStatus":"Success","Msg":"Map Updated"}

downloadtool avrdude https://downloads.arduino.cc/tools
�[34mINFO�[0m[0029] The filePrefix is avrdude-linux-amd64.zip 
�[34mINFO�[0m[0029] Downloading https://downloads.arduino.cc/tools/avrdude-linux-amd64.zip to /tmp/arduino-create-agent859167069/avrdude-linux-amd64.zip 
�[34mINFO�[0m[0030] 335444 bytes downloaded. 
�[31mERRO�[0m[0030] Could not unzip flashing tools! 
{"DownloadStatus":"Error","Msg":"exit status 1"}

checktool appears to be working

[ArduinoBot]

✅ Build completed.

Download at http://downloads.arduino.cc/CreateBridge/CreateBridge-PR69.zip

[matteosuppo]

Closing it because I incorporated some suggestions in another PR