spec/ruby: skip the specs that use /etc/passwd on Android

There is no /etc/passwd on Android

spec/ruby/core/file/stat/owned_spec.rb

@@ -21,7 +21,7 @@ describe "File::Stat#owned?" do
     st.owned?.should == true
   end
 
-  platform_is_not :windows do
+  platform_is_not :windows, :android do
     as_user do
       it "returns false if the file is not owned by the user" do
         system_file = '/etc/passwd'

spec/ruby/shared/file/executable.rb

@@ -13,7 +13,7 @@ describe :file_executable, shared: true do
     rm_r @file1, @file2
   end
 
-  platform_is_not :windows do
+  platform_is_not :windows, :android do
     it "returns true if named file is executable by the effective user id of the process, otherwise false" do
       @object.send(@method, '/etc/passwd').should == false
       @object.send(@method, @file1).should == true

spec/ruby/shared/file/readable.rb

@@ -4,9 +4,12 @@ describe :file_readable, shared: true do
     platform_is :windows do
       @file2 = File.join(ENV["WINDIR"], "system32/drivers/etc/services").tr(File::SEPARATOR, File::ALT_SEPARATOR)
     end
-    platform_is_not :windows do
+    platform_is_not :windows, :android do
       @file2 = "/etc/passwd"
     end
+    platform_is :android do
+      @file2 = "/system/bin/sh"
+    end
   end
 
   after :each do

spec/ruby/shared/file/writable.rb

@@ -8,7 +8,7 @@ describe :file_writable, shared: true do
   end
 
   it "returns true if named file is writable by the effective user id of the process, otherwise false" do
-    platform_is_not :windows do
+    platform_is_not :windows, :android do
       as_user do
         @object.send(@method, "/etc/passwd").should == false
       end