Do not echo y to lvconvert

This lvconvert is now able to complete operation automatically without question.
So remove  'echo y |'  - it's breaking pipe on some bash versions.

i.e.:
+ echo y
./t-lvconvert-mirror-basic.sh: line 104: echo: write error: Broken pipe

while command has completed this operation succesfully

test/t-lvconvert-mirror-basic.sh

@@ -101,7 +101,7 @@ test_lvconvert()
 		alloc="--alloc anywhere"
 	fi
 
-	echo y | lvconvert -m $finish_count --mirrorlog $finish_log_type \
+	lvconvert -m $finish_count --mirrorlog $finish_log_type \
 		$vg/$lv1 $alloc
 
 	if ! $active; then