adding convoy change for k8s client

[jimengliu]

@yasker

First part, it contains convoy changes in order to support k8s flex volume plugin, including daemon and API changes. It is supposed not to break existing convoy functionality.

• detach EBS volumes before attaching if they are not in-use
• expose File System type option to drivers when creating volumes
• add ReadWrite(ro, rw) mount options for all drivers
• add BindMount(-o bind) option for VFS driver that providing mountpoint
• add ReMount option together with BindMount option to allow a new mount point for k8s when it fails over a pod from one host to another

Second part, it contains k8s flex volume driver as a convoy client. There are some requirements from k8s driver side.

• driver must be a binary
• k8s invokes the driver with command(init, attach, detach, mount, unmount) as the first argument and then followed by command arguments in k8s format
• no stdout printout from driver at all except k8s required result status for each command
• Dependency:
• convoy daemon running with corresponding ebs and vfs drivers loaded

Second part code changes include:

• change build script to make a binary as a k8s volume driver plugin
• implement all required k8s volume plugin driver commands(init, attach, detach, mount, unmount) and k8s supported options
• driver uses rest API calls into convoy daemon to implement the functionalities inside convoy ebs/vfs drivers.
• a documentation file kubernetes.md to show how Flex Volume is defined by Kubernetes and how user can use this driver to integrate with Kubernetes

[yasker]

I don't see your comment here related to any of actual change of the code here.

You've introduced two new VolumeMountRequest and one more new field in VolumeCreateRequest, and at least one additional function for EBS to deal with volume attached on the other host. How can all these in one commit and without any explain of what's happened?

[jimengliu]

added more concrete comments related to changes

[yasker]

Close this one in favor of another solution.

[offlinehacker]

What is another solution?