Makefile tests exec: PTS files should not be hardcoded

[sansmoraxz]

modbus/Makefile

Lines 12 to 16 in 79617db

	test:
	diagslave -m tcp -p 5020 & diagslave -m enc -p 5021 & go test -run TCP -v $(shell glide nv)
	socat -d -d pty,raw,echo=0 pty,raw,echo=0 & diagslave -m rtu /dev/pts/1 & go test -run RTU -v $(shell glide nv)
	socat -d -d pty,raw,echo=0 pty,raw,echo=0 & diagslave -m ascii /dev/pts/3 & go test -run ASCII -v $(shell glide nv)
	go test -v -count=1 github.com/grid-x/modbus/cmd/modbus-cli

This may give issues viz say a shell terminal is already open using that path. This would polute their std io and look whole lot of ugly.