Custom HttpClient support

[SchutzeHades]

Hi, I noticed that this client uses org.apache.http.client.HttpClient and provides a constructor taking an HttpClientBuilder as a parameter. But in my situation, I want one more constructor that takes an org.apache.http.client.HttpClient as a parameter, because my http client is created by another library and there's no way to get that kind of builder object. Currently I extends org.kairosdb.client.HttpClient and replace the inner client using org.kairosdb.client.HttpClient#setClient method which is intended to be a test method. I suppose this may be a common situation and wonder if there are any plans to support this. Thank you.

[jsabin]

Fixed in 7b7fd3f in the development branch.