remove "wsk namespace get" command

@mbehrendt commented on [Fri Jun 24 2016](https://github.com/apache/incubator-openwhisk/issues/755)

`wsk namespace list` lists all namespaces, which is good.

`wsk namespace get ` seems to list all entities in a given namespace. however, when trying this out i always get the entities in the current namespace. besides that `wsk namespace get` seems to deliver the same results as `wsk list`, with the difference that `wsk namespace get` accepts the namespace to list as a parameter.

as an alternative, i'd suggest to eliminate `wsk namespace get`, and instead introduce sth like `wsk namespace switch-to `

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@rabbah commented on [Mon Jun 27 2016](https://github.com/apache/incubator-openwhisk/issues/755#issuecomment-228654456)

I'll guess that when you specified the `namespace` on `get` you omitted the leading `/` as in `wsk namespace get x` vs `wsk namespace get /x`. The leading `/` on an namespace is required in all CLI commands that refer to a namespace (rationale being that this indicates a change of a top level "path").

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@mbehrendt commented on [Mon Jun 27 2016](https://github.com/apache/incubator-openwhisk/issues/755#issuecomment-228672794)

`wsk namespace list` lists namespaces without the leading slash. so for consistency, i'd suggest we either list them with leading `/` or allow `wsk namespace get` to work with no leading `/`.

besides that -- i think think it's irritating to get the content of a different namespace listed when missing the `/` -- an error msg would be more appropriate.

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@csantanapr commented on [Wed Sep 07 2016](https://github.com/apache/incubator-openwhisk/issues/755#issuecomment-245326510)

tried in go-cli and doesn't matter what value I pass for NAMESPACE with / or without /
Also I think it should required user to specify leading `/`

```
$ wsk -v namespace get -h
get triggers, actions, and rules in the registry for a namespace
Usage:
wsk namespace get [NAMESPACE] [flags]

Global Flags:
--apihost HOST whisk API HOST
--apiversion VERSION whisk API VERSION
-u, --auth KEY authorization KEY
-d, --debug debug level output
-i, --insecure bypass certificate checking
-v, --verbose verbose output
```

Check current namespace

```
$ wsk property get --namespace
whisk namespace user@us.ibm.com_openwhisk
```

List namespaces

```
$ wsk namespace list
namespaces
user@us.ibm.com_dev
user@us.ibm.com_openwhisk
```

Try to get content for a specific namespace

```
$ wsk -v namespace get /csantana@us.ibm.com_dev

REQUEST:
[GET] https://openwhisk.ng.bluemix.net/api/v1/namespaces/user@us.ibm.com_openwhisk/
Req Headers
{
...
```

Try without leading `/`

```
$ wsk -v namespace get csantana@us.ibm.com_dev

REQUEST:
[GET] https://openwhisk.ng.bluemix.net/api/v1/namespaces/user@us.ibm.com_openwhisk/
Req Headers
{
...
```

try invalid namespace /foobar

```
REQUEST:
[GET] https://openwhisk.ng.bluemix.net/api/v1/namespaces/csantana@us.ibm.com_openwhisk/
Req Headers
{
...
```

It always uses the same value, and the input is never validated.

---

@dubeejw commented on [Wed Sep 07 2016](https://github.com/apache/incubator-openwhisk/issues/755#issuecomment-245380243)

@csantanapr, your issue will be address in https://github.com/openwhisk/openwhisk/pull/1211.

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@rabbah commented on [Thu Nov 16 2017](https://github.com/apache/incubator-openwhisk/issues/755#issuecomment-344954082)

a key is now unique to a namespace - so list returns only a singleton.
there is no switch operation supported in `wsk` since identity management is considered a separate concern.
we could delete `wsk namespace get` since it's probably not used given that we have `wsk list`.

@dubeejw @mdeuser thoughts?