Allow switching between oss and standard packages

Before only going from the standard package to oss was supported. Now
this works properly in both directions.

tasks/compatibility-variables.yml

@@ -14,6 +14,7 @@
     es_xpack_conf_subdir: ""
     es_repo_name: "{{ es_major_version }}"
     es_xpack_users_command: "elasticsearch-users"
+    es_other_package_name: "elasticsearch-oss"
 
 - name: Detect if es_version is before X-Pack was open and included
   set_fact:
@@ -33,6 +34,7 @@
   set_fact:
     es_repo_name: "{{ 'oss-' + es_major_version }}"
     es_package_name: "elasticsearch-oss"
+    es_other_package_name: "elasticsearch"
   when:
     - es_open_xpack
     - not es_enable_xpack