(testsuite) Fix _known_hosts_real

Clear COMPREPLY after test now that _known_hosts_real is appending
instead of setting COMPREPLY.

test/lib/library.sh

@@ -16,10 +16,13 @@ diff_env() {
 
 
 # Output array elements, sorted and separated by newline
+# Unset variable after outputting.
 # @param $1  Name of array variable to process
+# @param $2  -u (optional) Unset variable after echo
 echo_array() {
 	local IFS=$'\n'
-	eval echo \"\${$1[*]}\" | sort
+	eval printf "%s" \"\${$1[*]}\" | sort
+    unset -v $1
 }