Allow persisted couchdb directory mount.

For example:
  wskdev couchdb -d -e"db_persist_path=/home/couchd/openwhisk"

ansible/group_vars/all

@@ -236,6 +236,7 @@ db:
   protocol: "{{ db_protocol | default(lookup('ini', 'db_protocol section=db_creds file={{ playbook_dir }}/db_local.ini')) }}"
   port: "{{ db_port | default(lookup('ini', 'db_port section=db_creds file={{ playbook_dir }}/db_local.ini')) }}"
   host: "{{ db_host | default(lookup('ini', 'db_host section=db_creds file={{ playbook_dir }}/db_local.ini')) }}"
+  persist_path: "{{ db_persist_path | default(false) }}"
   instances: "{{ groups['db'] | length }}"
   authkeys:
   - guest

ansible/roles/couchdb/tasks/deploy.yml

@@ -15,6 +15,22 @@
   fail: msg="The db provider in your {{ hosts_dir }}/group_vars/all is {{ db.provider }}, it has to be CouchDB, pls double check"
   when: db.provider != "CouchDB"
 
+- name: ensure directory for persisting db exists
+  stat:
+    path: "{{ db.persist_path }}"
+  register: db_persist_path_exists
+  when: db.persist_path
+
+- name: fail if path to persist db does not exist
+  fail:
+    msg: directory for persisting db does not exist '{{ db.persist_path }}'
+  when: db.persist_path and not (db_persist_path_exists.stat.exists and db_persist_path_exists.stat.isdir)
+
+- name: "mount directory for persisting dbs"
+  set_fact:
+    volumes: "{{ volumes }} + [ '{{ db.persist_path }}:/opt/couchdb/data' ]"
+  when: db.persist_path
+
 - include_tasks: gen_erl_cookie.yml
   when: (db.instances|int >= 2)
 
@@ -52,7 +68,7 @@
   retries: 12
   delay: 5
 
-- name: create '_users' database for singleton mode
+- name: create '_users' database for singleton mode if necessary
   uri:
     url: "{{ db.protocol }}://{{ ansible_host }}:{{ db.port }}/_users"
     method: PUT