chore: Add tox configuration

Add tox configuration that allows to build a venv for development and to
format source files. To make use of it add appropriate Makefile targets.

Drop unneeded requirements from requirements.txt and
test-requirements.txt and add needed requirements.

Signed-off-by: Felix Matouschek <fmatouschek@redhat.com>

tox.ini

@@ -0,0 +1,22 @@
+[tox]
+env_list = venv
+
+[testenv:venv]
+download = True
+deps =
+    -r requirements.txt
+    -r test-requirements.txt
+    -r tests/requirements.txt
+allowlist_externals =
+    mkdir
+    ln
+commands =
+    mkdir -p "{env_site_packages_dir}/ansible_collections/kubevirt"
+    ln -sf "{tox_root}" "{env_site_packages_dir}/ansible_collections/kubevirt/core"
+    ansible-galaxy collection install -r requirements.yml -p "{env_site_packages_dir}/ansible_collections" --force
+
+[testenv:format]
+deps =
+    black
+commands = black .
+