TestShimOps: Change os.Stdin to pty.Open
TestShimOps: Change os.Stdin to pty.Open

Got some errors with test:
INFO[0000] Error getting size error="inappropriate ioctl for device" name=kata-shim pid=96301
INFO[0000] Error getting size error="inappropriate ioctl for device" name=kata-shim pid=96301
The reason is os.Stdin in test is not tty.

This patch replace os.Stdin with github.com/kr/pty.Open to handle the issues.

Signed-off-by: Hui Zhu <3dff0dee05fafb3e3012a2d92c6bc151ff61663b@hyper.sh>

amshinde/shim,amshinde/shim