Amplify installation fixes (#113)

* Remove syntax error

When evaluated (i.e. when nginx_amplify_enable=true and
nginx_amplify_api_key is defined) this line causes a syntax error

To check for empty string, opted for temporary solution outlined in ansible/ansible-lint#457

* Fix reference to amplify api key

Previously was labelled `amplify_api_key`. Changed to
`nginx_amplify_api_key` in #a55a50d

* Fix reference to default config file

On my system at least (bionic), the default configuration file is
`/etc/amplify-agent/agent.conf.default`

This is also assumed be to the case on the amplify install shell script https://github.com/nginxinc/nginx-amplify-agent/blob/master/packages/install.sh#L526

Author: cblanc

tasks/amplify/install-amplify.yml

@@ -13,12 +13,12 @@
 - name: "(Setup: All OSs) Copy NGINX Configurator Agent Configuration Template"
   copy:
     remote_src: yes
-    src: /etc/amplify-agent/agent.configurator.conf.default
-    dest: /etc/amplify-agent/agent.configurator.conf
+    src: /etc/amplify-agent/agent.conf.default
+    dest: /etc/amplify-agent/agent.conf
 
 - name: "(Setup: All OSs) Configure NGINX Amplify Agent API Key"
   lineinfile:
     dest: /etc/amplify-agent/agent.conf
     regexp: api_key =.*
-    line: "api_key = {{ amplify_api_key }}"
+    line: "api_key = {{ nginx_amplify_api_key }}"
   notify: "(Handler: All OSs) Start NGINX Amplify Agent"

tasks/main.yml

@@ -58,7 +58,7 @@
   when:
     - nginx_amplify_enable
     - nginx_amplify_api_key is defined
-    - nginx_amplify_api_key
+    - nginx_amplify_api_key | length > 0
 
 - import_tasks: controller/install-controller.yml
   when: