simplify test structure and add bin stubs

tests/bin/id

@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+
+echo "dokku"

tests/setup.sh

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 
-source "$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/unit/test_helper.bash"
+source "$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/test_helper.bash"
 
 if [[ ! -d $DOKKU_ROOT ]]; then
   git clone https://github.com/progrium/dokku.git $DOKKU_ROOT > /dev/null

tests/test_helper.bash

@@ -3,7 +3,7 @@
 export DOKKU_QUIET_OUTPUT=1
 export DOKKU_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/dokku"
 export DOKKU_VERSION=${DOKKU_VERSION:-"master"}
-export PATH="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/dokku:$PATH"
+export PATH="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/bin:$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/dokku:$PATH"
 export PLUGIN_PATH="$DOKKU_ROOT/plugins"
 export SERVICE=redis