Add scripts to make download, unzip and installation of source code easier

[houshengbo]

The first release of openwhisk consists of 13 repo packages. It is great help to distribute some scripts to automate the process of download, unzip and installation.

[rabbah]

At the very least, I suggest adding the command tar xvf openwhisk-0.9.0-incubating-sources.tar.gz to https://dist.apache.org/repos/dist/dev/incubator/openwhisk/apache-openwhisk-0.9.0-incubating-rc1/doc/INSTALL.md

[rabbah]

why not use wskdev fresh instead of the gradle and ansible steps - it will replace 8 terminal commands with just one.

@csantanapr cc