tools: Add option to pyboard.py to wait for serial device to be ready.
tools: Add option to pyboard.py to wait for serial device to be ready.

Also prints a nicer error message if the serial connection could not be
established.

infinnovation/micropython,lowRISC/micropython,xhat/micropython,galenhz/micropython,galenhz/micropython,Timmenem/micropython,toolmacher/micropython,mianos/micropython,torwag/micropython,praemdonck/micropython,infinnovation/micropython,pozetroninc/micropython,tralamazza/micropython,oopy/micropython,ganshun666/micropython,ryannathans/micropython,SHA2017-badge/micropython-esp32,puuu/micropython,hosaka/micropython,hiway/micropython,puuu/micropython,Peetz0r/micropython-esp32,adafruit/micropython,mianos/micropython,drrk/micropython,jmarcelino/pycom-micropython,misterdanb/micropython,jmarcelino/pycom-micropython,lowRISC/micropython,matthewelse/micropython,micropython/micropython-esp32,dmazzella/micropython,xhat/micropython,trezor/micropython,bvernoux/micropython,praemdonck/micropython,adamkh/micropython,praemdonck/micropython,mhoffma/micropython,MrSurly/micropython-esp32,matthewelse/micropython,blazewicz/micropython,toolmacher/micropython,trezor/micropython,cwyark/micropython,xhat/micropython,TDAbboud/micropython,tuc-osg/micropython,alex-robbins/micropython,lowRISC/micropython,oopy/micropython,EcmaXp/micropython,dinau/micropython,xhat/micropython,neilh10/micropython,praemdonck/micropython,dmazzella/micropython,MrSurly/micropython,MrSurly/micropython-esp32,trezor/micropython,ganshun666/micropython,alex-robbins/micropython,dinau/micropython,henriknelson/micropython,neilh10/micropython,cwyark/micropython,danicampora/micropython,swegener/micropython,torwag/micropython,dxxb/micropython,hiway/micropython,mpalomer/micropython,pfalcon/micropython,dmazzella/micropython,ernesto-g/micropython,HenrikSolver/micropython,martinribelotta/micropython,SHA2017-badge/micropython-esp32,infinnovation/micropython,selste/micropython,selste/micropython,supergis/micropython,alex-march/micropython,Peetz0r/micropython-esp32,matthewelse/micropython,MrSurly/micropython,martinribelotta/micropython,PappaPeppar/micropython,henriknelson/micropython,HenrikSolver/micropython,EcmaXp/micropython,SHA2017-badge/micropython-esp32,emfcamp/micropython,tralamazza/micropython,SHA2017-badge/micropython-esp32,toolmacher/micropython,chrisdearman/micropython,jmarcelino/pycom-micropython,galenhz/micropython,pramasoul/micropython,TDAbboud/micropython,pramasoul/micropython,adafruit/circuitpython,ryannathans/micropython,adamkh/micropython,adafruit/circuitpython,infinnovation/micropython,xhat/micropython,emfcamp/micropython,blazewicz/micropython,AriZuu/micropython,drrk/micropython,PappaPeppar/micropython,alex-march/micropython,chrisdearman/micropython,Peetz0r/micropython-esp32,swegener/micropython,lowRISC/micropython,henriknelson/micropython,pfalcon/micropython,turbinenreiter/micropython,EcmaXp/micropython,ernesto-g/micropython,misterdanb/micropython,hosaka/micropython,jmarcelino/pycom-micropython,MrSurly/micropython-esp32,misterdanb/micropython,redbear/micropython,kerneltask/micropython,kerneltask/micropython,tobbad/micropython,torwag/micropython,micropython/micropython-esp32,kerneltask/micropython,blazewicz/micropython,ryannathans/micropython,mianos/micropython,turbinenreiter/micropython,ryannathans/micropython,bvernoux/micropython,TDAbboud/micropython,torwag/micropython,deshipu/micropython,galenhz/micropython,adamkh/micropython,adafruit/circuitpython,bvernoux/micropython,hiway/micropython,AriZuu/micropython,dinau/micropython,tobbad/micropython,pfalcon/micropython,toolmacher/micropython,adamkh/micropython,Timmenem/micropython,dinau/micropython,hiway/micropython,PappaPeppar/micropython,danicampora/micropython,kerneltask/micropython,adafruit/circuitpython,alex-robbins/micropython,alex-march/micropython,puuu/micropython,adafruit/micropython,henriknelson/micropython,tuc-osg/micropython,bvernoux/micropython,PappaPeppar/micropython,martinribelotta/micropython,deshipu/micropython,tuc-osg/micropython,turbinenreiter/micropython,SHA2017-badge/micropython-esp32,adamkh/micropython,mpalomer/micropython,pozetroninc/micropython,torwag/micropython,dxxb/micropython,drrk/micropython,kerneltask/micropython,pfalcon/micropython,mpalomer/micropython,drrk/micropython,neilh10/micropython,ernesto-g/micropython,AriZuu/micropython,mianos/micropython,emfcamp/micropython,tobbad/micropython,mhoffma/micropython,swegener/micropython,Timmenem/micropython,blazewicz/micropython,Peetz0r/micropython-esp32,MrSurly/micropython-esp32,HenrikSolver/micropython,mhoffma/micropython,deshipu/micropython,pfalcon/micropython,trezor/micropython,deshipu/micropython,martinribelotta/micropython,mhoffma/micropython,mpalomer/micropython,tralamazza/micropython,dxxb/micropython,mpalomer/micropython,adafruit/circuitpython,trezor/micropython,bvernoux/micropython,puuu/micropython,Timmenem/micropython,micropython/micropython-esp32,misterdanb/micropython,martinribelotta/micropython,hosaka/micropython,ganshun666/micropython,henriknelson/micropython,Peetz0r/micropython-esp32,mhoffma/micropython,AriZuu/micropython,adafruit/micropython,oopy/micropython,oopy/micropython,hiway/micropython,mianos/micropython,matthewelse/micropython,dxxb/micropython,MrSurly/micropython,swegener/micropython,danicampora/micropython,praemdonck/micropython,neilh10/micropython,turbinenreiter/micropython,dmazzella/micropython,danicampora/micropython,misterdanb/micropython,chrisdearman/micropython,redbear/micropython,EcmaXp/micropython,infinnovation/micropython,tralamazza/micropython,tobbad/micropython,ernesto-g/micropython,TDAbboud/micropython,PappaPeppar/micropython,pozetroninc/micropython,chrisdearman/micropython,redbear/micropython,pramasoul/micropython,tuc-osg/micropython,hosaka/micropython,pramasoul/micropython,cwyark/micropython,toolmacher/micropython,matthewelse/micropython,danicampora/micropython,ganshun666/micropython,cwyark/micropython,ganshun666/micropython,micropython/micropython-esp32,redbear/micropython,HenrikSolver/micropython,AriZuu/micropython,ernesto-g/micropython,MrSurly/micropython-esp32,HenrikSolver/micropython,hosaka/micropython,jmarcelino/pycom-micropython,pramasoul/micropython,tobbad/micropython,neilh10/micropython,alex-robbins/micropython,supergis/micropython,selste/micropython,galenhz/micropython,chrisdearman/micropython,supergis/micropython,adafruit/micropython,alex-robbins/micropython,ryannathans/micropython,dinau/micropython,puuu/micropython,blazewicz/micropython,adafruit/micropython,pozetroninc/micropython,oopy/micropython,deshipu/micropython,alex-march/micropython,selste/micropython,cwyark/micropython,MrSurly/micropython,emfcamp/micropython,supergis/micropython,lowRISC/micropython,emfcamp/micropython,dxxb/micropython,matthewelse/micropython,alex-march/micropython,TDAbboud/micropython,micropython/micropython-esp32,selste/micropython,redbear/micropython,turbinenreiter/micropython,adafruit/circuitpython,MrSurly/micropython,swegener/micropython,Timmenem/micropython,EcmaXp/micropython,tuc-osg/micropython,drrk/micropython,supergis/micropython,pozetroninc/micropython