Add liveness probe

[leakingtapan]

Is this a bug fix or adding new feature?
Fixes: #159

What is this PR about? / Why do we need it?

What testing is done?

[k8s-ci-robot]

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[coveralls]

Pull Request Test Coverage Report for Build 486

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 67.773%

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Totals
Change from base Build 484:	0.0%
Covered Lines:	980
Relevant Lines:	1446

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💛 - Coveralls

[dkoshkin]

failureThreshold: 1 might be too aggressive, in their example they actually have 2:

failureThreshold: 5
...
failureThreshold: 1

[dkoshkin]

Looks like the test failures could have been caused because the the node driver restarted:

Logging pods the kubelet thinks is on node ip-172-20-50-17.us-west-2.compute.internal
Feb 26 02:54:34.076: INFO: kube-proxy-ip-172-20-50-17.us-west-2.compute.internal started at <nil> (0+0 container statuses recorded)
Feb 26 02:54:34.076: INFO: ebs-csi-node-xn2c8 started at 2019-02-26 02:33:06 +0000 UTC (0+3 container statuses recorded)
Feb 26 02:54:34.076: INFO: 	Container ebs-plugin ready: true, restart count 6

All 4 failures were on the volumes that take a long time to format and even if the formatting is attempted a second time, the 15 min timeout is not enough time.

[leakingtapan]

Notice the driver keeps being restarted many time even without any traffic due to probe timeout. Update the periodSeconds to 10s for less frequent probe, failureThreshold to 5 for higher failure tolerance. With the change, driver is back stable.

[bertinatto]

/lgtm