Enable rspec tests with reproducible test harness

Before this commit: chocolatey_spec.rb exists but is not runnable
After  this commit: run `rake spec` to perform unit tests

More info:

- Move existing chocolatey_spec.rb to a subdir so that we can
  keep rspec-related files in a single tree

- Use `bundle install` to add gem dependencies

- Configure this repo to push to tracking branch by default
Use travis-ci.org for continuous integration

Enable service hook to let travis-ci build the project [1].

[1] http://about.travis-ci.org/docs/user/getting-started/
Fix unit test to reflect current provider code

Commit 3ab91639 removed line feed from version number to fix
"version number resolution" in the provider code, but did not
change the associated rspec example.

This commit updates the rspec example to be consistent with
commit 3ab91639, and the unit test now passes:

Puppet::Type::Package::ProviderChocolatey when fetching a package list should return installed packages with their versions
Add env var to unit test

Commit 5c46d1e6 added a unit test that depends on an environment
variable, but the test raises an exception when the environment
variable does not exist.

Addresses:

    3) Puppet::Type::Package::ProviderChocolatey when fetching a package list should query chocolatey
    Failure/Error: commands=ENV['ChocolateyInstall'] + "/chocolateyInstall/chocolatey.cmd"
    NoMethodError:
    undefined method `+' for nil:NilClass
    # ./spec/unit/chocolatey_spec.rb:94
Align rspec expectations with code

The package provider receives 3 arguments, so
the rspec tests now expect 3 arguments.

Resolve failures such as:

    unexpected invocation:
    Package[chocolatey](provider=chocolatey).chocolatey('install', 'chocolatey', nil)
    unsatisfied expectations: - expected exactly once, not yet invoked:
    Package[chocolatey](provider=chocolatey).chocolatey('install', 'chocolatey')
Fix rspec test for querying chocolatey

* Fix existing test
* Add extra test

resolves:

    1) Puppet::Type::Package::ProviderChocolatey when fetching
    a package list should query chocolatey
       Failure/Error: provider.instances
       MiniTest::Assertion:
         unexpected invocation: Puppet::Type::Package::ProviderChocolatey.execpipe([nil, ' version all -lo ^| % { \\\'{0}=={1}\\\' -f $_.Name, $_.Found }'])
         unsatisfied expectations:
         - expected exactly once, not yet invoked: Puppet::Type::Package::ProviderChocolatey.execpipe()
         satisfied expectations:
         - allowed any number of times, not yet invoked: Facter.value(:osfamily)
         - allowed any number of times, not yet invoked: Facter.value(:operatingsystem)
         - allowed any number of times, not yet invoked: Puppet::Type::Package::ProviderChocolatey.healthcheck(any_parameters)
       # ./lib/puppet/provider/package/chocolatey.rb:63:in `instances'
       # ./spec/unit/chocolatey_spec.rb:106:in `block (3 levels) in <top (required)>'
use common style for spec tests

File cleanup:

* use 2-space soft tabs instead of hard tabs
* fix indents
* remove trailing whitespace
remove ruby 2.0 from travis build matrix

After this commit:

* `rake spec` is clean on:
  - ruby 1.8.7 (puppet 2.7 & puppet 3.1)
  - ruby 1.9.3 (puppet 2.7 & puppet 3.1)

* `rake spec` still fails on ruby 2.0 with...

    /home/travis/.rvm/gems/ruby-2.0.0-p0/gems/puppet-<version>/lib/puppet/util/autoload.rb:68:in
    `rescue in load_file': Could not autoload
    puppet/type/package: constant Puppet::Type::Package not
    defined (Puppet::Error)