Added environment support to the install buildpack process

- If a custom buildpack is being used chances are it's because there is something unique about the environment
- The most standard annoyance in enterprise environments is the lack of direct outbound connectivity
- Proxy support needs to be propogated during the entire end to end build process.
- http_proxy and https_proxy can be added as environment variables
- Custom buildpacks can use the environment variables to be proxy aware
- install-buildpack is now proxy aware; it simply loads the environment variables from ENV_DIR
Added ENV_DIR and Proxy support

git will pick up https_proxy and http_proxy if set and use those for the clone
Removed comment
Fixed variable escaping for $env_var
Restrict environment variables loaded

- Restrict to just proxt related environment variables
- Support upper and lowercase form
Removed whitespace
all: Move pkg/migrate into pkg/postgres

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
Merge pull request #546 from tlperkins/master

Proxy support
all: Move DB helpers into pkg/postgres

Signed-off-by: Lewis Marshall <lewis@lmars.net>
Merge pull request #556 from flynn/postgres-migrate

all: Move pkg/migrate into pkg/postgres
Merge pull request #557 from flynn/pkg-postgres-helpers

all: Move DB helpers into pkg/postgres
slugbuilder: Revert "Proxy support"

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
Merge pull request #558 from flynn/revert-546-master

slugbuilder: Revert "Proxy support"
Godeps: Switch to fork of github.com/docker/docker

Signed-off-by: Lewis Marshall <lewis@lmars.net>
Merge pull request #559 from flynn/godeps-fork-docker

Godeps: Switch to fork of github.com/docker/docker
Godeps: Update github.com/flynn/pq

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
controller: Use attempts when dialing hosts

Signed-off-by: Lewis Marshall <lewis@lmars.net>
test: Make Helper methods thread safe

Signed-off-by: Lewis Marshall <lewis@lmars.net>
Merge pull request #562 from flynn/scheduler-dial-host-attempts

controller: Use attempts when dialling hosts
Merge pull request #561 from flynn/test-helper-mtx

test: Make Helper methods thread safe