Some source files miss Apache license headers

Following [Apache license header guideline](http://www.apache.org/legal/src-headers.html), **all human-readable Apache-developed files that are included within a distribution must include the header text with few exceptions**. You can find few exceptions here: [which files do not require a license header](http://www.apache.org/legal/src-headers.html#faq-exceptions).

I used Apache Rat to check this repository after excluding a few files, and I got this report. We need to add Apache licensing header to those files.
```
Unapproved licenses:

openwhisk-client-go/tools/travis/setup.sh
openwhisk-client-go/tools/travis/build.sh
openwhisk-client-go/tools/travis/test_openwhisk.sh
openwhisk-client-go/Makefile
```

The excluded files are:
```
**/*.json
**/**.gradle
**/gradlew
**/gradle/**
**/.**
**/templates/**
**/*.j2.*
**/.github/**
**/auth.whisk.system
**/auth.guest
**/i18n_resources.go
```