There's several use cases for calling into ostree itself to do
mirroring, instead of using bare rsync. For example, it's a bit more
efficient as it doesn't require syncing the objects/ directory.
https://bugzilla.gnome.org/show_bug.cgi?id=728351
This uses gpgv for verification against DATADIR/ostree/pubring.gpg by
default. The keyring can be overridden by specifying OSTREE_GPG_HOME.
Add a unit test for commit signing with gpg key and verifying on pull;
to implement this we ship a test GPG key generated with no password
for Ostree Tester <test@test.com>.
Change all of the existing tests to disable GPG verification.