pt-summary shouldn't leave empty files; both summary tools should

die if passed a --save-samples directory that has files in it.

t/lib/bash/collect_system_info.sh

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 
-plan 39
+plan 40
 
 TMPDIR="$TEST_TMPDIR"
 PATH="$PATH:$PERCONA_TOOLKIT_SANDBOX/bin"
@@ -25,6 +25,13 @@ setup_commands
 
 collect_system_data "$p"
 
+p2="$TMPDIR/collect_mysql_info2"
+mkdir "$p2"
+touch "$p2/some_empty_file"
+collect_system_data "$p2"
+
+cmd_ok "test ! -e \"$p2/some_empty_file\"" "collect_system_data removes empty files before exiting"
+
 cat <<EOF > "$TMPDIR/expected"
 Fusion-MPT SAS
 EOF
@@ -181,7 +188,7 @@ test_linux_exclusive_collection () {
 
    is \
       "$(ls "${dir}/2" | grep 'lvs\|vgs\|netstat' | sort | xargs echo )" \
-      "lvs netstat vgs" \
+      "lvs lvs.stderr netstat vgs" \
       "linux_exclusive_collection: And works as expected if they are there"
 
    local i=1