Add a --generate-sizes option to commit to add size information to the
commit metadata. This will be used by higher level code which wants
to determine the total size necessary for downloading.
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.
Add an optional dependency on gpgme to add GPG signatures into the
detached metadata, with the key "ostree.gpgsigs", as an "aay", an
array of signatures (treated as binary data).
The commit command gains a --gpg-sign=<key-id> argument. Also add an
argument --gpg-homedir to set the GPG homedir where we look for
keyrings.