Fix debug test in Vagrantfile

Ever since env_logger started supporting colours, it doesn’t seem worth it to keep track of what is and isn’t in the log output. So just test that it doesn’t print nothing and call it a day.

xtests/debug

@@ -1,2 +0,0 @@
-DEBUG:exa::fs::file: Statting file "/testcases/attributes/dirs/no-xattrs_empty"
-INFO:exa::fs::dir: Reading directory "/testcases/attributes/dirs/no-xattrs_empty"

xtests/run.sh

@@ -276,8 +276,13 @@ $exa -lt  2>&1 | diff -q - $results/error_lt   || exit 1
 
 
 # Debug mode
-# (uses an empty directory so it prints nothing to stdout)
-EXA_DEBUG="1" $exa $testcases/attributes/dirs/no-xattrs_empty -lh 2>&1 | tail -n 2 | diff -q - $results/debug  || exit 1
+# What gets logged keeps changing, so instead of checking for an exact output,
+# list an empty directory and fail if nothing gets printed.
+DEBUG_OUT=$(EXA_DEBUG="1" $exa $testcases/attributes/dirs/no-xattrs_empty -lh 2>&1)
+if [ -z "$DEBUG_OUT" ]; then
+    echo "Debug test produced no output"
+    exit 1
+fi
 
 
 # And finally...