Ensures the auth modules are available with just require 'grpc'

- Also fixes some lint issues

src/ruby/lib/grpc.rb

@@ -27,6 +27,8 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+require 'grpc/auth/compute_engine.rb'
+require 'grpc/auth/service_account.rb'
 require 'grpc/errors'
 require 'grpc/grpc'
 require 'grpc/logconfig'

src/ruby/lib/grpc/auth/signet.rb

@@ -30,6 +30,7 @@
 require 'signet/oauth_2/client'
 
 module Signet
+  # Signet::OAuth2 supports OAuth2 authentication.
   module OAuth2
     AUTH_METADATA_KEY = :Authorization
     # Signet::OAuth2::Client creates an OAuth2 client

src/ruby/spec/auth/apply_auth_examples.rb

@@ -43,7 +43,6 @@ end
 WANTED_AUTH_KEY = :Authorization
 
 shared_examples 'apply/apply! are OK' do
-
   # tests that use these examples need to define
   #
   # @client which should be an auth client