Add e2e testing sandbox (#295)

This PR introduces new functionality for running e2e-tests in
k8s-cluster.

`make test` from a root invokes deploying of new sandbox for testing
cozystack.

from `packages/core/testing`:

`make test` - runs the end-to-end tests.
`make exec` - opens an interactive shell in the sandbox container.
`make login` - downloads the kubeconfig into a temporary directory and
runs a shell with the sandbox environment; mirrord must be installed.
`make proxy` - enables a SOCKS5 proxy; mirrord and gost must be
installed.

Signed-off-by: Andrei Kvapil <kvapss@gmail.com>

Makefile

@@ -8,6 +8,7 @@ build:
 	make -C packages/system/dashboard image
 	make -C packages/system/kamaji image
 	make -C packages/core/installer image
+	make -C packages/core/e2e image
 	make manifests
 
 manifests:
@@ -26,3 +27,7 @@ repos:
 
 assets:
 	make -C packages/core/installer/ assets
+
+test:
+	make -C packages/core/testing apply
+	make -C packages/core/testing test