Ansible 2.3 support

- Fix when clauses in various places
- Update requirements.txt
- Fix README.md

Signed-off-by: Sergii Golovatiuk <sgolovatiuk@mirantis.com>

roles/kernel-upgrade/tasks/reboot.yml

@@ -17,7 +17,7 @@
 
 - set_fact:
     wait_for_delegate: "{{hostvars['bastion']['ansible_ssh_host']}}"
-  when: "{{ 'bastion' in groups['all'] }}"
+  when: "'bastion' in groups['all']"
 
 - name: wait for bastion to come back
   wait_for:
@@ -27,7 +27,7 @@
     timeout: 300
   become: false
   delegate_to: localhost
-  when: "is_bastion"
+  when: is_bastion
 
 - name: waiting for server to come back (using bastion if necessary)
   wait_for:
@@ -37,4 +37,4 @@
     timeout: 300
   become: false
   delegate_to: "{{ wait_for_delegate }}"
-  when: "not is_bastion"
+  when: not is_bastion