This test had some nondeterminism because we chose a random
object to corrupt, but because there were multiple commits, it
was possible that we chose an object that was not being pulled.
Fix this by writing some custom GJS code to find an explicitly random
object that exists in a given ref, an change a random byte offset.
This adds a lot more randomness to the testing too.
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.
These corruption tests could be a lot better...like randomly try
single bit flips, range flips. Better, content-aware fuzzing. But
this is useful for now.