Invert the default value of enable_build_file_sandboxing.

Summary:
There is no reason for people to use this over the more fine grained
mechanisms for disabling it.

Test Plan:
CI
docs/soyweb-local.sh

Reviewed By: beefon

fbshipit-source-id: 1789deb

docs/concept/buckconfig.soy

@@ -2341,15 +2341,11 @@ your <code>.buckjavaargs</code> file</a>:
 {call buckconfig.entry}
   {param section: 'project' /}
   {param name: 'enable_build_file_sandboxing' /}
-  {param example_value: 'true' /}
+  {param example_value: 'false' /}
   {param description}
-    When set to <code>true</code> (the default is <code>false</code>), Buck will put restrictions
-    on importing arbitrary Python modules in {call buck.build_file /}s to make it harder to
-    accidentally violate assumptions about determinism of BUCK files and build rules. It will be
-    possible to import only whitelisted or sanitized modules, unrestricted import
-    behavior can be restored in a context by using
-    <a href="{ROOT}function/allow_unsafe_import.html"> <code>allow_unsafe_import()</code> </a>
-    function.
+    When set to <code>false</code> (the default is <code>true</code>), Buck will disable restrictions
+    on importing arbitrary Python modules in {call buck.build_file /}s which make it harder to
+    accidentally violate assumptions about determinism of BUCK files and build rules.
   {/param}
 {/call}
 

src/com/facebook/buck/parser/AbstractParserConfig.java

@@ -208,7 +208,7 @@ public ApplyDefaultFlavorsMode getDefaultFlavorsMode() {
 
   @Value.Lazy
   public boolean getEnableBuildFileSandboxing() {
-    return getDelegate().getBooleanValue("project", "enable_build_file_sandboxing", false);
+    return getDelegate().getBooleanValue("project", "enable_build_file_sandboxing", true);
   }
 
   @Value.Lazy

test/com/facebook/buck/parser/ParserConfigTest.java

@@ -217,7 +217,7 @@ public void shouldGetReadOnlyDirs() throws IOException {
 
   @Test
   public void testGetEnableBuildFileSandboxing() throws IOException {
-    assertFalse(
+    assertTrue(
         FakeBuckConfig.builder().build().getView(ParserConfig.class)
             .getEnableBuildFileSandboxing());