Fixed some problems, when same lua script using session handles different hosts/configurations

Session module creates a module local data structure, that contains initial configuration.
When lua code cache is enabled (default) the same module instance is used
for every request and it ends up using the same values from that data structure.

This patch fixes cookie.secure and cookie.domain, both of which can differ
when handling different requests.

However, to support different configurations - the entire session data structure
must be initialized differently. Perhaps allow the user to specify a key by which
a specific instance of session static data should be retrieved.
Or use a default host + ssl_session_id key.