Use __fake.?__ syntax for fake genrule outputs

These genrules do not produce an output file, instead they are run
by the developer to obtain their side-effects like building other
targets they happen to depend on.

Make it more clear these are fake by naming them __fake.?__, a name
we should never see appear in buck-out/.

Change-Id: Id749b095a0b2990f8d9c7e3942215fc7463a5255
diff --git a/BUCK b/BUCK
index eb5cfd9..6ad87f7 100644
--- a/BUCK
+++ b/BUCK
@@ -14,7 +14,7 @@
     ':extension-api',
     ':plugin-api',
   ],
-  out = '__api__',
+  out = '__fake.api__',
 )
 
 java_binary(name = 'extension-api', deps = [':extension-lib'])
@@ -59,7 +59,7 @@
     ':_eclipse_project',
     ':_eclipse_classpath',
   ],
-  out = 'eclipse',
+  out = '__fake.eclipse__',
 )
 
 genrule(
@@ -70,7 +70,7 @@
     ':_eclipse_project',
     ':_eclipse_classpath_nocompile',
   ],
-  out = 'eclipse',
+  out = '__fake.eclipse__',
 )
 
 java_library(
@@ -110,5 +110,5 @@
   cmd = '${//tools:eclipse_classpath}',
   srcs = [],
   deps = ['//tools:eclipse_classpath'],
-  out = '_eclipse_classpath_nocompile',
+  out = '__fake.eclipse__',
 )