Improve dumb terminal detection

When figuring out terminal type, check whether TERM=dumb is set.

Test: m nothing
Test: TERM=dumb m nothing
Test: m nothing | tee log
Change-Id: Ie13ca99eb84b798644d618ad1c8c1fb8ec8bb049

ui/terminal/util.go

@@ -23,6 +23,9 @@ import (
 )
 
 func isSmartTerminal(w io.Writer) bool {
+	if term, ok := os.LookupEnv("TERM"); ok && term == "dumb" {
+		return false
+	}
 	if f, ok := w.(*os.File); ok {
 		var termios syscall.Termios
 		_, _, err := syscall.Syscall6(syscall.SYS_IOCTL, f.Fd(),