tests: add coveralls support

Closes Homebrew/homebrew#47185.

Signed-off-by: Xu Cheng <xucheng@me.com>

Library/Homebrew/test/.simplecov

@@ -23,3 +23,8 @@ if name = ENV["HOMEBREW_INTEGRATION_TEST"]
     exit! exit_code
   end
 end
+
+if RUBY_VERSION.split(".").first.to_i >= 2 && !ENV["HOMEBREW_INTEGRATION_TEST"]
+  require "coveralls"
+  Coveralls.wear!
+end

Library/Homebrew/test/Gemfile

@@ -4,3 +4,4 @@ gem "mocha", "~> 1.1"
 gem "minitest", "~> 5.3"
 gem "rake", "~> 10.3"
 gem "simplecov", "~> 0.10.0", :require => false
+gem "coveralls", "0.8.9", :require => false

Library/Homebrew/test/Gemfile.lock

 GEM
   remote: https://rubygems.org/
   specs:
+    coveralls (0.8.9)
+      json (~> 1.8)
+      rest-client (>= 1.6.8, < 2)
+      simplecov (~> 0.10.0)
+      term-ansicolor (~> 1.3)
+      thor (~> 0.19.1)
+      tins (~> 1.6.0)
     docile (1.1.5)
     json (1.8.3)
     metaclass (0.0.4)
-    minitest (5.7.0)
+    mime-types (1.25.1)
+    minitest (5.8.3)
     mocha (1.1.0)
       metaclass (~> 0.0.1)
     rake (10.4.2)
+    rest-client (1.6.9)
+      mime-types (~> 1.16)
     simplecov (0.10.0)
       docile (~> 1.1.0)
       json (~> 1.8)
       simplecov-html (~> 0.10.0)
     simplecov-html (0.10.0)
+    term-ansicolor (1.3.2)
+      tins (~> 1.0)
+    thor (0.19.1)
+    tins (1.6.0)
 
 PLATFORMS
   ruby
 
 DEPENDENCIES
+  coveralls (= 0.8.9)
   minitest (~> 5.3)
   mocha (~> 1.1)
   rake (~> 10.3)
   simplecov (~> 0.10.0)
+
+BUNDLED WITH
+   1.11.2