test: check-multi-machine and check-dashboard for buggy Fedora 21
test: Disable check-storage testDosParts

And don't use extended partitions in other tests.

See https://bugzilla.redhat.com/show_bug.cgi?id=1135493
test: Work around freeipa-client bug in Fedora 21
test: Put new location of magic base tarballs into README.
test: Remove cockpit-selinux-policy package.

We get the policy from Fedora 21 now.
test: Don't let ipa-server-install block on /dev/random.