client SetScheme and SetHostURL causing the hostname to be invalid

[hendryang]

See #318

I have managed to get the reproduction step. It's mainly caused by SetScheme

func TestHostURLForGH318(t *testing.T) {

        // Notice that I'm using both SetScheme and SetHostURL in order to reproduce this issue.
	client := resty.New()
	client.SetScheme("https").SetHostURL("httpbin.org")

	fmt.Println("with leading `/`")
	resp, err := client.R().Post("/post")
	fmt.Println("Error:", err)
	fmt.Println("Response:", resp)

	fmt.Println("\nwithout leading `/`")
	resp, err = client.R().Post("post")
	fmt.Println("Error:", err)
	fmt.Println("Response:", resp)

	fmt.Println()
	fmt.Println("with leading `/` on request")
	fmt.Println("with trailing `/` on host url")
	client.SetHostURL("https://httpbin.org/")
	resp, err = client.R().Post("/post")
	fmt.Println("Error:", err)
	fmt.Println("Response:", resp)
}

Error from first and second request:

with leading `/`
Error: Post "https://httpbin.org%2Fpost/httpbin.org/post": dial tcp: lookup httpbin.org/post: no such host
Response: 

without leading `/`
Error: Post "https://httpbin.org%2Fpost/httpbin.org/post": dial tcp: lookup httpbin.org/post: no such host
Response: 

[moorereason]

client.SetScheme("https").SetHostURL("httpbin.org")

Resty should somehow do the right thing here (or at least not do the wrong thing), but the API assumes that the SetHostURL parameter will contain the scheme. Don't mix SetScheme and SetHostURL.

[jeevatkm]

@hendryang I have fixed the issue. Can you please try this branch for-gh318-gh407 and share your feedback?