commands/operator-sdk/cmd/local: add namespace flag

[jhernandezb]

ref: #273

This adds the --namespace flag to the up local command and the default value is the "default" namespace.

Example:

operator-sdk up local --namespace operator

Help output

$ operator-sdk up local --help
The operator-sdk up local command launches the operator on the local machine
by building the operator binary with the ability to access a
kubernetes cluster using a kubeconfig file.

Usage:
  operator-sdk up local [flags]

Flags:
  -h, --help                    help for local
      --kubeconfig string       The file path to kubernetes configuration file; defaults to $HOME/.kube/config
      --namespace string        The namespace where the operator watches for changes. (default "default")
      --operator-flags string   The flags that the operator needs. Example: "--flag1 value1 --flag2=value2"

[fanminshi]

I am debating whether should we add a short named flag for namespace because none of the other flags have a short version.

I'd suggest we don't add it now. Maybe we can revisit adding the short flags in a future pr.

Suggest to avoid using the word will and keep description in present tense: The namespace where the operator will watch. -> The namespace where the operator watches for changes?

[fanminshi]

Could you also update the https://github.com/operator-framework/operator-sdk/blob/master/CHANGELOG.md to include this change?

Just modify Added operator-sdk up command ... to incorporate this change.

[jhernandezb]

I've applied the changes please take a look.

[fanminshi]

reference #274 after #219

[jhernandezb]

done

[fanminshi]

lgtm after nits