Adds checkcov to the build

[bowei]

Adds a simple script for checking code coverage

`checkcov` takes as input the output of "go test -cover ..." and a checkcov
YAML file containing expected coverage limits.

Usage

$ go test -cover ./pkg/...  > cov.out
$ go run tools/checkcov.go -configFile checkcov.yaml -covFile cov.out

[bowei]

@swetharepakula

[google-oss-prow[bot]]

@swetharepakula: changing LGTM is restricted to collaborators

In response to [this](https://github.com/GoogleCloudPlatform/k8s-cloud-provider/pull/146#pullrequestreview-1707316450): > Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.

[google-oss-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bowei, swetharepakula

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/GoogleCloudPlatform/k8s-cloud-provider/blob/master/OWNERS)~~ [bowei] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[swetharepakula]

/lgtm

[google-oss-prow[bot]]

@swetharepakula: changing LGTM is restricted to collaborators

In response to [this](https://github.com/GoogleCloudPlatform/k8s-cloud-provider/pull/146#issuecomment-1788116086): > > >/lgtm Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.

[swetharepakula]

/lgtm

[google-oss-prow[bot]]

@swetharepakula: changing LGTM is restricted to collaborators

In response to [this](https://github.com/GoogleCloudPlatform/k8s-cloud-provider/pull/146#issuecomment-1788116917): >/lgtm Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.

[spencerhance]

/lgtm