Fix string replacement in certutil http test (#69404)

This test had 2 issues:
1. It performed a replacement using a string literal on a randomly
generated string. It is possible that the filename had ".csr"
somewhere in the basename, which would then produce incorrect results
2. It used the wrong base file for the substitution (key vs csr).

This fixes the bug by using an index based replacement rather than a
textual one.

Backport of: #69319

Author: tvernum

x-pack/plugin/security/cli/src/test/java/org/elasticsearch/xpack/security/cli/HttpCertificateCommandTests.java

@@ -185,10 +185,11 @@ public void testGenerateSingleCertificateSigningRequest() throws Exception {
         // Verify the key
         assertMatchingPair(getPublicKey(csr), privateKey);
 
-        final String crtName = keyPath.getFileName().toString().replace(".csr", ".crt");
+        final String csrName = csrPath.getFileName().toString();
+        final String crtName = csrName.substring(0, csrName.length() - 4) + ".crt";
 
         // Verify the README
-        assertThat(esReadme, containsString(csrPath.getFileName().toString()));
+        assertThat(esReadme, containsString(csrName));
         assertThat(esReadme, containsString(crtName));
         assertThat(esReadme, containsString(keyPath.getFileName().toString()));
         assertThat(esReadme, containsString(ymlPath.getFileName().toString()));
@@ -197,7 +198,7 @@ public void testGenerateSingleCertificateSigningRequest() throws Exception {
         }
 
         // Verify the yml
-        assertThat(yml, not(containsString(csrPath.getFileName().toString())));
+        assertThat(yml, not(containsString(csrName)));
         assertThat(yml, containsString(crtName));
         assertThat(yml, containsString(keyPath.getFileName().toString()));
         if ("".equals(password) == false) {
@@ -210,7 +211,7 @@ public void testGenerateSingleCertificateSigningRequest() throws Exception {
         // No CA in CSR mode
         verifyKibanaDirectory(zipRoot, false,
             Collections.singletonList("Certificate Signing Request"),
-            Stream.of(password, csrPath.getFileName().toString())
+            Stream.of(password, csrName)
             .filter(s -> "".equals(s) == false).collect(Collectors.toList()));
     }