MINOR: http: Add a function to get the authority into a URI

The function http_get_authority() may be used to parse a URI and looks for the
authority, between the scheme and the path. An option may be used to skip the
user info (part before the '@'). Most of time, the user info will be ignored.
diff --git a/include/common/http.h b/include/common/http.h
index fbbc33c..857c66e 100644
--- a/include/common/http.h
+++ b/include/common/http.h
@@ -136,6 +136,7 @@
 enum http_meth_t find_http_meth(const char *str, const int len);
 int http_get_status_idx(unsigned int status);
 const char *http_get_reason(unsigned int status);
+struct ist http_get_authority(const struct ist uri, int no_userinfo);
 struct ist http_get_path(const struct ist uri);
 int http_header_match2(const char *hdr, const char *end,
                        const char *name, int len);