Removes unused "server" from taskmanager

Reasons:
- server has not got any proper used-case in the code.
- Methods for server creation do not need to return server.

Changes
- Removes server from return of server creation methods.
- Removes server from FreshInstanceTasks.create_instance.

Closes-Bug: #1265896
Change-Id: I729992a7f5124d4a6da12835a08b07e38b583f61
Merge "Removes unused "server" from taskmanager"