jshell tests affect command shell windows

[Jonathan Gibbons]

Kulla team,

Using the latest jdk9/dev bits, if I run the langtools/test/jdk/jshell 
tests, my terminal window becomes corrupted, such that no printable 
characters are echoed, and "return" just displays the prompt echaracters 
repeatedly on the same line.

A reset command clears the condition, but this is still a pretty serious 
problem.

-- Jon