Enable krb5kdc-fixture, kerberos tests mount urandom for kdc container

Infra has fixed elastic#10462 by installing `haveged` on CI workers.
This commit enables the disabled fixture and tests, and mounts
`/dev/urandom` for the container so there is enough
entropy required for kdc.

Closes elastic#40624

Author: Yogesh Gaikwad

test/fixtures/krb5kdc-fixture/build.gradle

@@ -47,8 +47,7 @@ postProcessFixture {
     }
 }
 
-// https://github.com/elastic/elasticsearch/issues/40624
-buildFixture.enabled = false
+buildFixture.enabled = true
 
 project.ext.krb5Conf = { service -> file("$buildDir/shared/${service}/krb5.conf") }
 project.ext.krb5Keytabs = { service, fileName -> file("$buildDir/shared/${service}/keytabs/${fileName}") }

test/fixtures/krb5kdc-fixture/docker-compose.yml

@@ -8,6 +8,7 @@ services:
     command: "bash /fixture/src/main/resources/provision/peppa.sh"
     volumes:
       - ./build/shared/peppa:/fixture/build
+      - /dev/urandom:/dev/random
     ports:
       - "4444"
       - "88/udp"
@@ -19,6 +20,7 @@ services:
     command: "bash /fixture/src/main/resources/provision/hdfs.sh"
     volumes:
       - ./build/shared/hdfs:/fixture/build
+      - /dev/urandom:/dev/random
     ports:
       - "4444"
       - "88/udp"

x-pack/qa/kerberos-tests/build.gradle

@@ -8,8 +8,7 @@ apply plugin: 'elasticsearch.test.fixtures'
 
 testFixtures.useFixture ":test:fixtures:krb5kdc-fixture"
 
-// https://github.com/elastic/elasticsearch/issues/40624
-integTest.enabled = false
+integTest.enabled = true
 
 dependencies {
     testCompile "org.elasticsearch.plugin:x-pack-core:${version}"
@@ -56,9 +55,9 @@ integTestCluster {
 String realm = "BUILD.ELASTIC.CO"
 integTestRunner {
     Path peppaKeytab = Paths.get("${project.buildDir}", "generated-resources", "keytabs", "peppa.keytab")
-    systemProperty 'test.userkt', "peppa@${realm}"
-    systemProperty 'test.userkt.keytab', "${peppaKeytab}"
-    systemProperty 'test.userpwd', "george@${realm}"
+    nonInputProperties.systemProperty 'test.userkt', "peppa@${realm}"
+    nonInputProperties.systemProperty 'test.userkt.keytab', "${peppaKeytab}"
+    nonInputProperties.systemProperty 'test.userpwd', "george@${realm}"
     systemProperty 'test.userpwd.password', "dino"
     systemProperty 'tests.security.manager', 'true'
     jvmArgs([