Initialize app search client with bearer_auth flag

[gaoruifeng]

http_flag gives warning message: DeprecationWarning: The 'http_auth' parameter is deprecated. Use 'basic_auth' or 'bearer_auth' parameters instead as discussed in #158

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[sethmlarson]

jenkins test this please

[nkammah]

run docs-build