Rename redo to wskdev

Currently there is a [redo][1] script which simplifies the development workflow. However most of time we refer it as `wskdev` with a [symbolic link][2] in bin directory

While it was added in #834 an alias was added to existing `redo` tooling. However the docs in the readme still refer to it as redo. We should reword the docs to wskdev (probably rename the redo script also) to remove the confusion

[1]: https://github.com/apache/incubator-openwhisk/blob/ccac7d5131a80bddeb1b6dc0c6580051c90bc264/tools/build/README.md#how-to-use-redo
[2]: https://github.com/apache/incubator-openwhisk/blob/ccac7d5131a80bddeb1b6dc0c6580051c90bc264/bin/wskdev

Start with the “How to use redo” section in tools/build/README.md and inspect bin/wskdev, then compare the referenced redo script and its symbolic-link relationship. Done means the documentation consistently refers to wskdev and the script naming no longer causes confusion.

Written by the indexing model from the issue text.