create provider for sakuracloud(Japan) (Relpace of #2625)

This PR is replace of #2625.

rebase to master and squash commits following:

```
list ssh_keys and create disk
add models and requests for  create computer
create server at once
add bin and route file
update create_with
write getting_started wip. and create helper methods.
add sakura to mock_helper
add bin and route file
write getting_started wip. and create helper methods.
add mocks and test
create tests and write getting started
writenig provider for sakuracloud ,wip
list ssh_keys and create disk
add models and requests for  create computer
create server at once
add bin and route file
update create_with
write getting_started wip. and create helper methods.
add sakura to mock_helper
add bin and route file
write getting_started wip. and create helper methods.
add mocks and test
create tests and write getting started
mv getting_started to docs
mv getting_started to docs
use snake_case for models
fix: wrong usage of :aliases
update doc. replace to snake_case from class
update mocks format
Fix: remove commas for Ruby 1.8.7
duplicate example
use create method with option if atatch volume
remove empty line (checking travis works..)
fix args for core/provider.rb#service
```