DEA advertises how many instances it has of each app
Clone a single revision

Previously, when a buildpack was cloned, the entire buildpack
repository was fetched.  This resulted in a slower clone than was
otherwise necessary.  This change executes the clone with a --depth 1
which only fetches a single revision and no history.  This results in
noticeable speed gains.

Buildpack                       Full    Depth 1
===============================================
cloudfoundry-buildpack-java:    2.031s  1.451s
heroku-buildpack-nodejs:        6.840s  1.577s
heroku-buildpack-ruby:          5.075s  1.785s

[#50080879]
Initialize buildpack submodules

Previously, when a buildpack was cloned, any submodules containted
within that repository were not initialized.  This means that any
split of buildpack code across repositories was difficult if not
impossible.  This change adds --recurse-submodules to the clone
command to initialize any declared submodules.

[#50081011]
Merge pull request #22 from nebhale/50080879-depth-1

Clone a single revision
Merge pull request #23 from nebhale/50081011-submodules

Initialize buildpack submodules
loosen up .ruby-version (don't specify patchlevel)
Loosen em timeout requirements for travis
DEA won't start app instances it doesn't have the capacity for

[fixes #50202171]
Fix buildpack clone incompatibility (bug introduced by pull request)
Change app instance exit reason to "app instance exited"
DEA no longer snapshots it's entire state of what instances are running, we'll let health manager start any of the instances back up in the normal manner
refactor resource rollup computations out into the individual registries, instead of having the resource manager grope into them
register the instance right away when creating, don't wait for it to change states [fixes #50202171]
Generate app event when app startup sequence fails
Better logging and error message for instance health check
Bump vcap_common
Publish stacks to /varz

[#48362877]
send shutdown message when the dea is exiting

this can be picked up by other components (CC, HM) to invalidate the DEA
from their advertisements, and know not to send apps there

[#50233251]
fix specs for new dea shutdown message