tests/containers/fips-nginx: fix typos and add trap in build.sh

Fixes #4477

Author: HuijingHei

tests/containers/fips-nginx/README.md

@@ -1,6 +1,6 @@
 # fips-nginx Container
 
-This is used by the `fips.enable.https` test to verify that using
+This is used by the `fips.enable.tls` test to verify that using
 TLS works in FIPS mode by having Ignition fetch a remote resource
 over HTTPS with FIPS compatible algorithms.
 

tests/containers/fips-nginx/build.sh

@@ -14,7 +14,9 @@ fi
 ip="$1"
 
 tmpdir="$(mktemp -d)"
-cp Containerfile ${tmpdir}
+trap 'rm -rf -- "${tmpdir}"' EXIT
+
+cp Containerfile "${tmpdir}"
 cd ${tmpdir}
 
 # Prepare index.html