test-bot: start running generic tests. (Homebrew#505)

* test-bot: start running generic tests.

Start running the test suite in the "generic" mode i.e. a base layer for
non-OS X platforms to be able to use to ensure we don't break the generic code
for the parts of the code we've got running.

Currently this just runs the integration tests as that's the only useful suite
that's entirely passing but eventually this will be changed to run the full test
suite in generic mode.

* test_integration_cmds: fix tests on Linux.

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

@@ -664,6 +664,8 @@ def homebrew
           tests_args << "--coverage" if ENV["TRAVIS"]
         end
         test "brew", "tests", *tests_args
+        test "brew", "tests", "--generic", "--only=integration_cmds",
+                              *tests_args
         test "brew", "tests", "--no-compat"
         test "brew", "readall", "--syntax"
       else

Library/Homebrew/test/test_integration_cmds.rb

@@ -358,7 +358,7 @@ def test_edit
 
   def test_sh
     assert_match "Your shell has been configured",
-                 cmd("sh", "SHELL" => "/usr/bin/true")
+                 cmd("sh", "SHELL" => which("true"))
   end
 
   def test_info
@@ -588,10 +588,7 @@ def test_prune
     assert((share/"notpruneable").directory?)
     refute((share/"pruneable_symlink").symlink?)
 
-    # Inexact match because only if ~/Applications exists, will this output one
-    # more line with contents `No apps unlinked from /Users/<user/Applications`.
-    assert_match "Nothing pruned\nNo apps unlinked from /Applications",
-      cmd("prune", "--verbose")
+    assert_match "Nothing pruned", cmd("prune", "--verbose")
   end
 
   def test_custom_command