KASM-1942 Ensure we retry the agent connection check to give time for webapp startup

roles/install_common/tasks/agent_install.yml

@@ -3,6 +3,10 @@
     url: "https://{{ web_ip }}/api/__healthcheck"
     timeout: 5
     validate_certs: false
+  register: _result
+  until: _result.status == 200
+  retries: 7
+  delay: 5
 
 - name: Install agent role
   command: "bash {{ tempdir.path }}/kasm_release/install.sh -S agent -e -p {{ target_ip }} -m {{ web_ip }} -M {{ manager_token }}"