Add releaseTest option to CI script (elastic/x-pack-elasticsearch#2482)

This option runs a normal check but with `-Dsnapshot=false` (the flag
used to indicate a release build).

Related to https://github.com/elastic/infra/issues/2759 and
https://github.com/elastic/infra/issues/2739 from the ES side.

Original commit: elastic/x-pack-elasticsearch@e674e68905

dev-tools/ci

@@ -57,6 +57,16 @@ case $key in
             "-Dtests.badapples=true"
         )
         ;;
+    releaseTest)
+        GRADLE_CLI_ARGS=(
+            "--info"
+            "check"
+            "-Dtests.network=true"
+            "-Dtests.badapples=true"
+            "-Dbuild.snapshot=false"
+            "-Dtests.jvm.argline=-Dbuild.snapshot=false"
+        )
+        ;;
     jdk9)
         GRADLE_CLI_ARGS=(
             "-Pxpack.kibana.build=false"