Added example for the API Mangement service

[WilliamMortlMicrosoft]

This PR adds an additional example for this repo that demonstrates how to add/delete an API Management Service as well as add/delete an API endpoint within the service.

NOTE: this test takes a VERY long time to run (~60m) due to the speed (or lack thereof) with which Azure creates an API Management service instance.

[WilliamMortlMicrosoft]

Successful test run example:

Williams-MBP:apimgmt wmortl$ go test -timeout 60m
2019/08/29 15:06:01 creating resource group 'azure-samples-go-APIMSTest-jVhoN' on location: eastus2
2019/08/29 15:06:07 creating api management service...
creating api management service...
2019/08/29 15:45:19 api management service created
api management service created
2019/08/29 15:45:19 creating api endpoint...
creating api endpoint...
2019/08/29 15:46:28 open api endpoint created
open api endpoint created
2019/08/29 15:46:28 deleting the api endpoint...
deleting the api endpoint...
2019/08/29 15:46:31 open api endpoint deleted
open api endpoint deleted
2019/08/29 15:48:33 api management service deleted
api management service deleted
2019/08/29 15:48:33 deleting resources
PASS
ok github.com/WilliamMortlMicrosoft/azure-sdk-for-go-samples/apimgmt 2554.421s

[WilliamMortlMicrosoft]

The test is set to t.SkipNow() due to the length of it running... that line can be commented out in order to run it manually. This test takes too long to be part of a continuous integration pipeline.

[WilliamMortlMicrosoft]

Please fix the build error, it is not due to this PR:

WARNING: failed to install github.com/golang/lint/golint: exit status 1

gometalinter: error: failed to install the following linters: github.com/golang/lint/golint

WARNING: exec: "golint": executable file not found in $PATH

done linting.

building...

github.com/Azure-Samples/azure-sdk-for-go-samples/web

github.com/Azure-Samples/azure-sdk-for-go-samples/vendor/github.com/Azure/azure-sdk-for-go/services/web/mgmt/2016-09-01/web

github.com/Azure-Samples/azure-sdk-for-go-samples/web

done building.

ISPR: 1

Makefile:2: recipe for target 'test' failed

make: *** [test] Error 1```

[jhendrixMSFT]

Module name needs to be fixed. You might also just omit the go.mod/go.sum files for now as we don't have great module support at this time.

[WilliamMortlMicrosoft]

Thanks for the review @jhendrixMSFT !! I made your suggested changes and added a README file