pull: Add a --dry-run option for static deltas

One of the design goals with deltas was not just wire efficiency,
but also having all the data up front about how much data would
be transferred before starting.

Let's expose that better by adding a `dry-run` option to the pull API.
This requires static deltas to be useful.  Basically we simply call
the progress callback once with the data from the superblock.

tests/pull-test.sh

@@ -107,12 +107,24 @@ rm main-files -rf
 # Generate delta that we'll use
 ${CMD_PREFIX} ostree --repo=ostree-srv/gnomerepo static-delta generate main
 prev_rev=$(ostree --repo=ostree-srv/gnomerepo rev-parse main^)
+new_rev=$(ostree --repo=ostree-srv/gnomerepo rev-parse main)
 ostree --repo=ostree-srv/gnomerepo summary -u
 
+cd ${test_tmpdir}
+repo_init
+${CMD_PREFIX} ostree --repo=repo pull origin main@${prev_rev}
+${CMD_PREFIX} ostree --repo=repo pull --dry-run --require-static-deltas origin main >out.txt
+assert_file_has_content out.txt 'Delta update: 0/1 parts'
+rev=$(${CMD_PREFIX} ostree --repo=repo rev-parse origin:main)
+assert_streq "${prev_rev}" "${rev}"
+${CMD_PREFIX} ostree --repo=repo fsck
+
 cd ${test_tmpdir}
 repo_init
 ${CMD_PREFIX} ostree --repo=repo pull origin main@${prev_rev}
 ${CMD_PREFIX} ostree --repo=repo pull --require-static-deltas origin main
+rev=$(${CMD_PREFIX} ostree --repo=repo rev-parse origin:main)
+assert_streq "${new_rev}" "${rev}"
 ${CMD_PREFIX} ostree --repo=repo fsck
 
 cd ${test_tmpdir}
@@ -140,6 +152,8 @@ fi
 assert_file_has_content err.txt "deltas required, but none found"
 ${CMD_PREFIX} ostree --repo=repo fsck
 
+echo "ok delta required but don't exist"
+
 cd ${test_tmpdir}
 rm main-files -rf
 ${CMD_PREFIX} ostree --repo=ostree-srv/gnomerepo checkout main main-files