Create the basic Travis environment

[houshengbo]

This PR empowers the project with the following features:

• Add the support to define the list of repos to be released
  and the hash value to be picked for each repo in a config file of
  JSON format define the hash value

• Download the repos based on the definitions in the config file.

• Install openwhisk based on the dowloaded source code, build the
  binaries for CLI and wskdeploy.

[mrutkows]

Apparently, you cannot wait for 65 minutes...

$ ./tools/travis/setup.sh
hello openwhisk release
$ travis_wait 66 ./tools/travis/build.sh
Still running (49 of 66): ./tools/travis/build.sh
The job exceeded the maximum time limit for jobs, and has been terminated.

[houshengbo]

@mrutkows That is the problem. We should either get rid of the time limit, or use other build environment.

[houshengbo]

The Travis build can be split into several jobs, running either in parallel or sequential, so we can bypass the 50-min time limit issue.

@mrutkows I think this PR can be the foundation to start our further work.
Currently, it proves that we are able to define the repos and hash values in JSON file, travis is able to download source code, and build based on the source code.