Remove unused scripts

This change removes `start-test-agent` and `reload-bpm` from the scripts
directory. It also updates the `CONTRIBUTING.md` to instruct users to
run the acceptance tests using the `bosh-lite-acceptance-test` script.

This change also updates the `test-with-concourse` to work with newer
versions of concourse.

CONTRIBUTING.md

@@ -52,10 +52,8 @@ $ cd bpm-release
 $ ./scripts/test-with-docker
 ```
 
-2. To run the acceptance tests against docker
+2. To run the acceptance tests against bosh-lite
 ```bash
 $ cd bpm-release
-$ ./scripts/start-docker # this will launch you into the docker shell
-/go# /bpm/scripts/start-test-agent
-/go# ginkgo -r -p -race /bpm/src/bpm/acceptance -- --agent-uri="http://127.0.0.1:1337"
+$ ./scripts/bosh-lite-acceptance-test
 ```

scripts/test-with-concourse

@@ -4,9 +4,8 @@ absolute_path() {
   (cd $1 && pwd)
 }
 
+FLY_TARGET=${FLY_TARGET:-ci}
+
 scripts_path=$(absolute_path `dirname $0`)
 
-fly -t ci execute \
-  -x \
-  -p \
-  -c ${scripts_path}/../ci/test-unit.yml "$@"
+fly -t ${FLY_TARGET} execute -p -c ${scripts_path}/../ci/test-unit.yml "$@"