Add newline character when writing offline to block device state

[pwschuurman]

What type of PR is this?
/kind bug

What this PR does / why we need it:
This PR adds "\n" character to the disable device command (when writing to /sys/block/<devX>/device/state). Currently the command emits invalid argument (but the error is ignored).

Which issue(s) this PR fixes:
Fixes #1146

Special notes for your reviewer:

Without this fix, the prog.out in e2e test prints out:

W0404 01:22:27.876675   49081 node.go:460] Failed to disabled device /dev/disk/by-id/google-gcepd-csi-e2e-b3c295b8-24d2-4804-b363-385a66c7ffd0 (aka /dev/sdj) for volume projects/psch-gke-dev/zones/us-east4-c/disks/gcepd-csi-e2e-b3c295b8-24d2-4804-b363-385a66c7ffd0. Device may not be detached cleanly (ignored, unstaging continues): write /sys/block/sdj/device/state: invalid argument

Validated that with this fix, this warning is not printed.

Does this PR introduce a user-facing change?:

Bugfix: Correctly disable device by writing `offline`

[pwschuurman]

/retest

[pwschuurman]

/retest

[mattcary]

Nice find!

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mattcary, pwschuurman

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[pwschuurman]

/retest

[k8s-ci-robot]

@pwschuurman: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-gcp-compute-persistent-disk-csi-driver-kubernetes-integration	33bc37f	link	true	/test pull-gcp-compute-persistent-disk-csi-driver-kubernetes-integration

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[k8s-ci-robot]

PR needs rebase.

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[pwschuurman]

Closing. We decided to remove the disable device logic in #1689