Skip download of Hadoop / ZK SNAPSHOT tarballs (#350)

This is a minor change to skip downloading such tarballs. Previously,
attempting to use (for example) hadoop-x.y.z-SNAPSHOT.tar.gz would fail
as the download task attempts to get that tarball from the ASF mirror.
diff --git a/ansible/roles/proxy/tasks/download.yml b/ansible/roles/proxy/tasks/download.yml
index 446336e..798b665 100644
--- a/ansible/roles/proxy/tasks/download.yml
+++ b/ansible/roles/proxy/tasks/download.yml
@@ -26,6 +26,7 @@
     - { urlp: "{{ apache_mirror.stdout }}/hadoop/common/hadoop-{{ hadoop_version }}", fn: "{{ hadoop_tarball }}", sum: "{{ hadoop_checksum }}" }
     - { urlp: "{{ apache_mirror.stdout }}/maven/maven-3/{{ maven_version }}/binaries", fn: "{{ maven_tarball }}", sum: "{{ maven_checksum }}" }
     - { urlp: "https://github.com/github/hub/releases/download/v{{ hub_version }}", fn: "{{ hub_tarball }}", sum: "{{ hub_checksum }}" }
+  when: "'snapshot' not in item.fn.lower()"
 
 # This is currently needed to run hadoop with Java 11 (see https://github.com/apache/fluo-muchos/issues/266)
 - name: "Download javax.activation-api for Hadoop 3 when Java 11 is used"