Cleans up ServiceUser.__str__ method

Reasons:
- ServiceUser.__str__ in trove/tests/util/users.py contains code
  after the return statement.
- This code after unconditional return statement has no use.
- Thus, ServiceUser.__str__ method needs cleanup.

Changes:
- Removes the statements after return statement.
- Adds tenant name to the __str__.

Change-Id: Ic5e35969f435e01d94da7eb434cd8de19e2c9873
Closes-Bug: #1269437
Remove admin_token from configs

A previous review removed the admin_token from the sample config file.
It appears that devstack doesn't use that file but instead uses one of
the .test files.

Admin tokens are actively discouraged as a form of authenticating in
auth_token middleware and the behaviour when using admin_token in
combination with a username and password (as this default produces in
devstack) can lead to problems in authentication.

Closes-Bug: #1299332
Change-Id: I78d2c184f7937006b808d580e3663ab055f7c5fe
Merge "Cleans up ServiceUser.__str__ method"
Merge "Remove admin_token from configs"
Add stack_id to base instance model

Reasons:
 - saving stack id would give to trove an
   ability to perform actions such as
   stack update/delete;

Changes:
 - adding stack_id column into base schema;
 - DBInstance model update.

Change-Id: I193c15e72f93cc3fe5be72a41a1ad23d93e04047
Implements: blueprint stack-id
Refactor taskmanager. Split heat/native/migration code path

Reasons:
 - Trove should be able to manage resource provisioning through:
    - nova, cinder, designate etc. (navites);
    - heat. (orchestration).
    - Main reason is to provide harmless migration from the nova to heat,
      when heat would be cover all required use cases such as
      provisioning/resizing/network-attributes-management.

Changes:
- Refactoring:
  - dividing actual manager onto navite(nova/cinder/designate/neutron)
    and orchestrator(heat);
  - extracting common code into taskmanager/common.py
  - fixing tests;
  - Resize instance for orchestrator added;
  - Resize volume for orchestrator added.

Change-Id: Ibdab5cb78bc2a83112fe9813b7effd6e0dd0a503
Implements: blueprint resource-manager-interface