disable caching in tests

Some tests have errors due to too long file names:
test_show(Groups::HomeControllerTest):
ActionView::Template::Error: File name too long - /home/travis/build/Crabgrass/Crabgrass-Core/tmp/cache/views%2Ftest.host%2Fgroups%2Frsdalbertoarrell%2Fhome%3Flang%3Den%26may_admin%3Dtrue%26updated_at%3D1361578688%26version%3D1%26what%3Dcommittees11691-host%2Fgroups%2Frsdalbertoarrell%2Fhome%3Flang%3Den%26may_admin%3Dtrue%26updated_at%3D1361578688%26version%3D1%26what%3Dcommittees.lock
    /home/travis/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/tempfile.rb:346:in 'rmdir'

We'll have to look into caching separately