CLOUDSTACK-5660: Migrate vm live migration succeeds but throws error as "Failed to migrate the system vm".
Fix mock socket client/server test.

Normally a server will bind to 0.0.0.0, which is not an
address that a client can specify to connect to.
127.0.0.1 or ::1 will do.
Some rework stratosphere ssp plugin

* add missing command entry in commands.properties
* migrate httpclient 3.x to 4.x
* fix the broken SspClient
* add webapp session checking in mock ssp server