Fixed installation issue with kube-flannel.yml

The installation of the local K8s cluster fails when kube-flannel.yml
is not found in the temp folder. The error that we see in the installation is
"error reading [/tmp/flannel.*****]: recognized file extensions are [.json .yaml .yml]"

This commit updates the function deploy_cni_provider to remove the silent
output when getting kube-flannel.yml. In addition, it adds several retries on error.
Finally, the error message has been modified to be more explicit about the error.

Change-Id: Ie979dc599d959bed778b3bd1e2c69257fcb51f63
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>