There is a wrong directory path to all.yml and vsphere.yml. The wrong directory is `inventory/sample/group_vars/all.yml` and `inventory/sample/group_vars/all/vsphere.yml` which should be `inventory/sample/group_vars/all/all.yml` and `inventory/sample/group_vars/all/vsphere.yml`.

* Fix invalid link to Ansible documentation

* Fix invalid link to mitogen doc page

* Fix invalid link to calico doc page

* Fix all invalid links to doc pages

* Added possibility to specify vSphere credentials via env variables

* Removed excessive spacing

Signed-off-by: Rui Cao <ruicao@alauda.io>

fix typo