[rubygems/rubygems] Remove unnecessary nesting from standalone specs

Originally, all the specs in this file were put inside a shared examples
block, and since then all specs were run only changing the cwd (either
from root, or a subdirectory).

This was in ruby/rubygems@d7291700d016, to cover a fix in
the `bundler_path` method.

However, reverting that fix does not make any of the specs in either of
the main blocks fail! Only an unrelated spec of `bundle install
--standalone --local` fails.

The reason is that all specs set `path` to an absolute path, making the
fix essentially uncovered.

In order to simplify the file structure and improve runtime, I
completely removed the shared examples block, and only run main specs
for the root directory. Then I added a couple of extra specs to cover
the original bug fix.

This cuts runtime of this spec file in half, from 1m30s to 45s on my
laptop.

ruby/rubygems@cc506f17e0

Author: deivid-rodriguez

spec/bundler/install/gems/standalone_spec.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-RSpec.shared_examples "bundle install --standalone" do
+RSpec.describe "bundle install --standalone" do
   shared_examples "common functionality" do
     it "still makes the gems available to normal bundler" do
       args = expected_gems.map {|k, v| "#{k} #{v}" }
@@ -237,6 +237,8 @@
     end
   end
 
+  let(:cwd) { bundled_app }
+
   describe "with Gemfiles using relative path sources and app moved to a different root" do
     before do
       FileUtils.mkdir_p bundled_app("app/vendor")
@@ -511,16 +513,33 @@
   end
 end
 
-RSpec.describe "bundle install --standalone" do
-  let(:cwd) { bundled_app }
-
-  include_examples("bundle install --standalone")
-end
-
 RSpec.describe "bundle install --standalone run in a subdirectory" do
   let(:cwd) { bundled_app("bob").tap(&:mkpath) }
 
-  include_examples("bundle install --standalone")
+  before do
+    gemfile <<-G
+      source "https://gem.repo1"
+      gem "rails"
+    G
+  end
+
+  it "generates the script in the proper place" do
+    bundle :install, standalone: true, dir: cwd
+
+    expect(bundled_app("bundle/bundler/setup.rb")).to exist
+  end
+
+  context "when path set to a relative path" do
+    before do
+      bundle "config set --local path bundle"
+    end
+
+    it "generates the script in the proper place" do
+      bundle :install, standalone: true, dir: cwd
+
+      expect(bundled_app("bundle/bundler/setup.rb")).to exist
+    end
+  end
 end
 
 RSpec.describe "bundle install --standalone --local" do