entrypoint.sh: Ensure exit code is from flawfinder

Ensure that the returned exit code is from flawfinder, not
another tool (like "tee").

Signed-off-by: David A. Wheeler <dwheeler@dwheeler.com>

entrypoint.sh

@@ -2,4 +2,10 @@
 # $1 whitespace-separated arguments. Some filenames may need to be escaped.
 # $2 output filename
 
-flawfinder $1 | tee "$2"
+output="${2:-flawfinder-output.txt}"
+
+flawfinder $1 > "$output"
+result="$?"
+
+cat "$output"
+exit "$result"