Reduce the log level of cinder-csi-driver

[ialidzhikov]

/kind enhancement
/platform openstack

As described in #287, the csi-driver-node logging is verbose and noisy.

Except the livenessprobe container, the csi-driver container is noisy as well. It generates a lot of logs such as:

I0524 20:01:44.879641       1 utils.go:81] GRPC request:
I0524 20:01:44.879674       1 identityserver.go:50] Probe() called with req
I0524 20:01:44.885084       1 utils.go:86] GRPC response:
I0524 20:01:54.879767       1 utils.go:80] GRPC call: /csi.v1.Identity/Probe
I0524 20:01:54.879837       1 utils.go:81] GRPC request:
I0524 20:01:54.879872       1 identityserver.go:50] Probe() called with req
I0524 20:01:54.883811       1 utils.go:86] GRPC response:
I0524 20:02:04.879962       1 utils.go:80] GRPC call: /csi.v1.Identity/Probe
I0524 20:02:04.879978       1 utils.go:81] GRPC request:
I0524 20:02:04.880007       1 identityserver.go:50] Probe() called with req
I0524 20:02:04.884123       1 utils.go:86] GRPC response:

Release note:

NONE

[vpnachev]

/lgtm