Change GCE sysctls placement and docs

Override GCE sysctl in /etc/sysctl.d/99-sysctl.conf instead of
the /etc/sysctl.d/11-gce-network-security.conf. It is recreated
by GCE, f.e. if gcloud CLI invokes some security related changes,
thus losing customizations we want to be persistent.

Update cloud providers firewall requirements in calico docs.

Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>

roles/kubernetes/preinstall/tasks/main.yml

@@ -71,7 +71,7 @@
 
 - name: Fix ipv4 forward rule in GCE security policy
   lineinfile:
-    dest: /etc/sysctl.d/11-gce-network-security.conf
+    dest: /etc/sysctl.d/99-sysctl.conf
     regexp: '^net.ipv4.ip_forward='
     line: 'net.ipv4.ip_forward=1'
     state: present