Add drvier libguestfs to support deploy more operator system,
you can use it by edit host config file add 'image_deploy_driver: libguestfs'.
By the default host-deploy support run three guestfish at the same time.
And host deployer will recycle free guestfish every ten minitues.
cherrypick: release/3.6
* fix(esxi): Fetch full templates of datastoreImageCache
Datastore 和 DatastoreImageCache 是一对一的关系。
每一个 Datastore 可能有多个对应的 Host，所以 GetIIMages 里面获取
Templates 的逻辑应该尝试去获取所有 Host 的 Templates。
* fix(host-deployer): Exit correctly after mounting
MountRootfs的返回值为nil时，还是需要Umount的操作来正确退出（比如VDDK）。
VDDK的Mount分为两步，第一步会挂在remote
disk到fuse下，然后挂载fuse/xxx/flat
到块设备上。第一步成功，第二部失败也应该正确退出。
* fix(host-deployer): Kill process
* opt(host-deployer): Increase timeout of waiting mount
* opt(host-deployer): Add debug log print command to mount
* fix(esxi): Support multi agent in different zone
1. 修改了host-deployer 使其支持 vmware vddk 的 deploy guest fs 操作。
2. esxi agent python ==> Go
fix(esxi-agent): Fix some bugs and irregular contents
fix(esxi-agent): Partial parameter structure
fix(esxi-agent): Add ovf template and remove some binary file
fix(esxi-agent): Format Code
fix(esxi-agent): fix based on reviewers' comments
fix(esxi-agent): fix host-deployer because of occasional unknown panic
fix: DelayTask should have a new Context
fix(esxi-agent): call hostutils.DelayTask
change '_interface' package to 'iagent' package
fix(esxi-agent): Fix some irregular code
guoguangwu