docs: upgrading kubernetes version

* Upgrading kubernetes version to 1.12.0.
  Connects reanahub/reana-cluster/issues/140

Signed-off-by: Rokas Maciulaitis <rokas.maciulaitis@cern.ch>

docs/administratorguide.rst

@@ -184,13 +184,14 @@ Local deployment using Minikube
 REANA cloud uses `Kubernetes <https://kubernetes.io/>`_ container orchestration
 system. The best way to try it out locally is to set up `Minikube
 <https://kubernetes.io/docs/getting-started-guides/minikube/>`_ (minikube
-version 0.28.2 is known to work the best).
+version 0.32.0 is known to work the best).
 
 The minikube can be started as follows:
 
 .. code-block:: console
 
-   $ minikube start --kubernetes-version="v1.11.2"
+   $ minikube start --kubernetes-version="v1.12.1" \
+     --feature-gates="TTLAfterFinished=true"
 
 REANA cluster can be easily deployed by means of the ``reana-cluster`` helper
 script. The typical usage scenario goes as follows:

docs/gettingstarted.rst

@@ -50,9 +50,10 @@ You can also easily deploy your own REANA cloud instance by using the
 
 .. code-block:: console
 
-   $ # install kubectl 1.11.2 and minikube 0.28.2
+   $ # install kubectl 1.13.1 and minikube 0.32.0
    $ sudo dpkg -i kubectl*.deb minikube*.deb
-   $ minikube start --kubernetes-version="v1.11.2"
+   $ minikube start --kubernetes-version="v1.12.1" \
+     --feature-gates="TTLAfterFinished=true"
    $ # create new virtual environment
    $ virtualenv ~/.virtualenvs/myreana
    $ source ~/.virtualenvs/myreana/bin/activate

reana/cli.py

@@ -155,7 +155,8 @@ def cli():  # noqa: D301
 
         \b
         $ # install minikube and set docker environment
-        $ minikube start --kubernetes-version="v1.11.2" --vm-driver=kvm2
+        $ minikube start --kubernetes-version="v1.12.1" --vm-driver=kvm2 \
+          --feature-gates="TTLAfterFinished=true"
         $ eval $(minikube docker-env)
         $ # option (a): cluster in production-like mode
         $ reana-dev docker-build