Use rspec-retry in flaky brew tests.

We have a few tests that are intermittently flaky. Let's try this to see
if we can get them a bit more reliable.

Library/Homebrew/test/Gemfile

@@ -5,6 +5,7 @@ require_relative "../constants"
 gem "parallel_tests"
 gem "rspec"
 gem "rspec-its", require: false
+gem "rspec-retry", require: false
 gem "rspec-wait", require: false
 gem "rubocop", HOMEBREW_RUBOCOP_VERSION
 

Library/Homebrew/test/Gemfile.lock

@@ -31,6 +31,8 @@ GEM
     rspec-mocks (3.6.0)
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.6.0)
+    rspec-retry (0.5.6)
+      rspec-core (> 3.3, < 3.8)
     rspec-support (3.6.0)
     rspec-wait (0.0.9)
       rspec (>= 3, < 4)
@@ -58,9 +60,10 @@ DEPENDENCIES
   parallel_tests
   rspec
   rspec-its
+  rspec-retry
   rspec-wait
   rubocop (= 0.52.1)
   simplecov
 
 BUNDLED WITH
-   1.16.0
+   1.16.1

Library/Homebrew/test/cmd/search_spec.rb

@@ -25,7 +25,7 @@ describe "brew search", :integration_test do
       .and be_a_success
   end
 
-  it "falls back to a GitHub tap search when no formula is found", :needs_network do
+  it "falls back to a GitHub tap search when no formula is found", :needs_network, retry: 3 do
     expect { brew "search", "caskroom/cask/firefox" }
       .to output(/firefox/).to_stdout
       .and output(/Searching/).to_stderr

Library/Homebrew/test/cmd/services_spec.rb

@@ -1,4 +1,4 @@
-describe "brew services", :integration_test, :needs_macos, :needs_network do
+describe "brew services", :integration_test, :needs_macos, :needs_network, retry: 3 do
   it "allows controlling services" do
     setup_remote_tap "homebrew/services"
 

Library/Homebrew/test/dev-cmd/pull_spec.rb

@@ -6,7 +6,7 @@ describe "brew pull", :integration_test do
       .and be_a_failure
   end
 
-  it "fetches a patch from a GitHub commit or pull request and applies it", :needs_network do
+  it "fetches a patch from a GitHub commit or pull request and applies it", :needs_network, retry: 3 do
     CoreTap.instance.path.cd do
       system "git", "init"
       system "git", "checkout", "-b", "new-branch"

Library/Homebrew/test/spec_helper.rb

@@ -2,6 +2,7 @@ require "find"
 require "pathname"
 require "rspec/its"
 require "rspec/wait"
+require "rspec/retry"
 require "rubocop"
 require "rubocop/rspec/support"
 require "set"