Make spec pass more resiliently

Previously, if bundler-2.1.0.pre.1 would be installed globally, it would
fail. Now we force that a locally installed version of bundler is used,
so it always passed regardless of which bundler is installed globally.

spec/runtime/setup_spec.rb

@@ -109,7 +109,7 @@
     def clean_load_path(lp)
       without_bundler_load_path = ruby!("puts $LOAD_PATH").split("\n")
       lp = lp - without_bundler_load_path
-      lp.map! {|p| p.sub(/^#{Regexp.union system_gem_path.to_s, default_bundle_path.to_s}/i, "") }
+      lp.map! {|p| p.sub(/^#{Regexp.union system_gem_path.to_s, default_bundle_path.to_s, lib.to_s}/i, "") }
     end
 
     it "puts loaded gems after -I and RUBYLIB", :ruby_repo do
@@ -136,6 +136,8 @@ def clean_load_path(lp)
     end
 
     it "orders the load path correctly when there are dependencies" do
+      system_gems :bundler
+
       install_gemfile <<-G
         source "#{file_uri_for(gem_repo1)}"
         gem "rails"
@@ -151,6 +153,7 @@ def clean_load_path(lp)
 
       expect(load_path).to start_with(
         "/gems/rails-2.3.2/lib",
+        "/gems/bundler-#{Bundler::VERSION}/lib",
         "/gems/activeresource-2.3.2/lib",
         "/gems/activerecord-2.3.2/lib",
         "/gems/actionpack-2.3.2/lib",