Add tmp dir in actionview/test/

Missing tmp directory will cause the test to fail on JRuby. will commit
adds tmp directory & 22 TemplateDigestorTests which were failing before
are now green.

Further Discussion on this can be seen at #11743
Merge pull request #11743 from gaurish/tmp-magic

[Jruby] Make all tests in ActionView::TemplateDigestorTest green