wsk CLI needs a flag to query its version

@uwefassnacht commented on [Tue Apr 25 2017](https://github.com/apache/incubator-openwhisk/issues/2178)

How do I know which version of the CLI I have installed? And whether it's the latest & greatest one? How do I know when to update (re-install) the CLI?

It would be good to provide a `-v` flag (similar to the cloud foundry CLI) that outputs the version. I realize that `-v`is already taken (verbose option).

At the very least, the CLI "splash screen" (displayed when using `wsk` without any options) should display a version number.

It's also not clear from the CLI repo at https://openwhisk.ng.bluemix.net/cli/go/download what the current version is and whether it's time to update.

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@sjfink commented on [Tue Apr 25 2017](https://github.com/apache/incubator-openwhisk/issues/2178#issuecomment-297032707)

`wsk property get --cliversion`

probably duplicate of https://github.com/openwhisk/openwhisk/issues/1492

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@rabbah commented on [Tue Apr 25 2017](https://github.com/apache/incubator-openwhisk/issues/2178#issuecomment-297045811)

@houshengbo @pritidesai as part of making the JSON object available advertising the CLIs versions, it would be nice to address the comment above: the link to a binary should carry version information.

Of course, we don't have a proper version yet or release tag (#1880).
@csantanapr I think we need one epic to track all the related CLI issues for versioning, the download page, etc.

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@eweiter commented on [Tue Apr 25 2017](https://github.com/apache/incubator-openwhisk/issues/2178#issuecomment-297047369)

It would also be nice if we could try to expose this info through the CLI page on the download button or near it.

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@dubeejw commented on [Tue Apr 25 2017](https://github.com/apache/incubator-openwhisk/issues/2178#issuecomment-297120898)

@eweiter, @houshengbo, we should be able to expose the CLI version to the UI via the content.json file.