Add a raw output option to a property queried with "wsk property get"

@l2fprod commented on [Mon Nov 14 2016](https://github.com/apache/incubator-openwhisk/issues/1503)

When called with no arguments, `wsk property get` shows a table like output:

```
whisk auth BLAH
whisk API host openwhisk.ng.bluemix.net
whisk API version v1
whisk namespace frederic.lavigne@fr.ibm.com_openwhisk-vision
whisk CLI version 2016-10-24T11:55:02+00:00
whisk API build 2016-11-08T13:28:31Z
whisk API build number whisk-build-1683
```

Let's say I want to retrieve the namespace, I can use `wsk property get --namespace`. This output:

```
whisk namespace frederic.lavigne@fr.ibm.com_openwhisk-vision
```

Now I have to parse this output to isolate the namespace. This leads to extra `awk` calls like we can see in several advanced OpenWhisk tutorials https://github.com/IBM-Bluemix/openwhisk-darkvisionapp/blob/master/processing/deploy-darkvision.sh, https://github.com/skaegi/openwhisk-package-pipeline/blob/master/deploy.sh

This would go away if the output of the get command was exactly the value of the property with no extra formatting sugar. So instead of
```
CURRENT_NAMESPACE=`wsk property get --namespace | awk '{print $3}'`
```
I would just do
```
CURRENT_NAMESPACE=`wsk property get --namespace`
```
More readable and less error prone - what if OpenWhisk decides to change the formatting of the output adding more words or spaces, my $3 would no longer match the namespace.