Terraform init -upgrade flag (#4455) (#4502)

* Adds optional `-upgrade` flag to terraform init.

This allows Terraform to install provider dependencies into an existing project when the provider constraints change.

* fix transposed documentation keys

* Add integration tests for terraform init

* Revert to validate_certs: yes for general public testing

* skip integration tests on irrelevant platforms

* skip legacy Python versions from CI tests

* add changelog fragment

* Update plugins/modules/cloud/misc/terraform.py

Adds version_added metadata to the new module option.

Co-authored-by: Felix Fontein <felix@fontein.de>

* Change terraform_arch constant to Ansible fact mapping

* correct var typo, clarify task purpose

* Squashed some logic bugs, added override for local Terraform

If `existing_terraform_path` is provided, the playbook will not download Terraform or check its version.

I also tested this on a local system with Terraform installed, and squashed some bugs related to using of an
existing binary.

* revert to previous test behavior for TF install

* readability cleanup

* Update plugins/modules/cloud/misc/terraform.py

Co-authored-by: Felix Fontein <felix@fontein.de>
(cherry picked from commit e4a25beedc)

Co-authored-by: Kamil Markowicz <geekifier@users.noreply.github.com>

tests/integration/targets/terraform/aliases

@@ -0,0 +1,7 @@
+shippable/posix/group1
+skip/windows
+skip/aix
+skip/osx
+skip/macos
+skip/freebsd
+skip/python2