Addition of basic auth support

[matthewsullivan-wf]

Following the pattern defined in splunk/splunk-sdk-ruby#43, I have implemented Basic Auth in this PR.

from splunklib.client import Service

service = Service(host="splunk.myhost.net", port=8089, scheme="https", version=6.3,
                  basic=True, username="steve", password="puppydoge")

service.indexes['test'].submit("My message!", host="localhost", sourcetype="text")

[matthewsullivan-wf]

@itay any idea what I'm doing wrong getting this test set up?
https://travis-ci.org/splunk/splunk-sdk-python/jobs/98574591#L602

[matthewsullivan-wf]

@itay ^

[itay]

Hey @matthewsullivan-wf - sorry it took so long to reply. I finally had some time to look today.

Anyway, I found the issue with your test. I put a comment on the specific line, but I wanted to ask you how you wanted to proceed. I can merge your PR once that's fixed (and if you want to rebase it to the tip of develop and squash your commits), or I can just fix it and get that merged. I wanted to give you the option of doing it yourself so you get "credit" for the contribution on GitHub, since you did the hard work :)

Let me know how you want to proceed.

[itay]

You're trying to log in with a bad set of credentials. Change this line to:

        opts["username"] = self.opts.kwargs["username"]
        opts["password"] = self.opts.kwargs["password"]

[sullivanmatt]

@itay appreciate the consideration for credit, but I don't care - I just need it fixed so we can start using the SDK at my place of work :) Go ahead if you've got everything staged that you need.

[itay]

Superceded by #133