Scope timeout to Ovh.Client instance

[Luke Marlin]

Timeout param currently works in a strange way.
Ovh.Client._httpClient is static and instantiated at the first construction of an Ovh.Client.
During that first instantiation, _httpClient.Timeout is set to Ovh.Client constuctor's timeout param.

It means that during subsequent instantiations, the timeout param is effectively ignore.