recipes::default: Add Sentry configuration file.
Vagrantfile: Rename VM to sentry-lucid.

This change is in preparation for introducing other VM images into the
Vagrantfile for testing multiple OS targets.
Vagrantfile: Work around vagrant#2281.

The Chef file cache location was changed at some point in the recent
past which exposed a race condition during initial provisioning.  The
workaround is to reset `chef.file_cache_path` to its old value.  An
alternative would be to create and share a cache from host to VM.  That
is probably a better solution and will be considered in the future.
sentry::default: Remove installation of setuptools.

It turns out that the python-setuptools package is not strictly
necessary for this recipe to work so it has been removed from the
recipe.
Add supervisor dependency.
recipes::default: Add supervisor support.
Rakefile: Clean up.

The berks:install task is better written using the `Berkshelf` module
directly instead of shelling out to the *berks* utility.  The
maintainer-clean task is better expressed using %q{} quoting instead of
single quotes.
Rakefile: Add spec:integration task.
unit tests: Add create_if_missing_template.
recipes::default: Add CentOS support.

The supervisor cookbook does not include explicit support for RedHat
based operating systems.  It installs the Python package by leaves out
service creation and management.  The sentry cookbook adds the missing
steps for CentOS.