Tests: Use small timeouts for server selection tests in http.txt

This tries to improve timing behaviour/flakyness on CI.

References: #404, 575f6a3

src/crate/client/doctests/http.txt

@@ -24,7 +24,7 @@ When using a list of servers, the servers are selected by round-robin::
 
  >>> invalid_host = "invalid_host:9999"
  >>> even_more_invalid_host = "even_more_invalid_host:9999"
- >>> http_client = HttpClient([crate_host, invalid_host, even_more_invalid_host])
+ >>> http_client = HttpClient([crate_host, invalid_host, even_more_invalid_host], timeout=0.3)
  >>> http_client._get_server()
  'http://127.0.0.1:44209'
 
@@ -36,17 +36,18 @@ When using a list of servers, the servers are selected by round-robin::
 
 Servers with connection errors will be removed from the active server list::
 
- >>> http_client = HttpClient([invalid_host, even_more_invalid_host, crate_host])
+ >>> http_client = HttpClient([invalid_host, even_more_invalid_host, crate_host], timeout=0.3)
  >>> result = http_client.sql('select name from locations')
  >>> http_client._active_servers
  ['http://127.0.0.1:44209']
 
 Inactive servers will be re-added after a given time interval.
-To validate this, set the interval very short and sleep for that interval::
+To validate this, set the interval and timeout very short and sleep after the first request::
 
  >>> http_client.retry_interval = 1
- >>> import time; time.sleep(1)
  >>> result = http_client.sql('select name from locations')
+ >>> import time; time.sleep(1)
+ >>> server = http_client._get_server()
  >>> http_client._active_servers
  ['http://invalid_host:9999',
  'http://even_more_invalid_host:9999',
@@ -55,7 +56,7 @@ To validate this, set the interval very short and sleep for that interval::
 If no active servers are available and the retry interval is not reached, just use the oldest
 inactive one::
 
- >>> http_client = HttpClient([invalid_host, even_more_invalid_host, crate_host])
+ >>> http_client = HttpClient([invalid_host, even_more_invalid_host, crate_host], timeout=0.3)
  >>> result = http_client.sql('select name from locations')
  >>> http_client._active_servers = []
  >>> http_client._get_server()