OSTree Support

When doing a copy from one ostree repo to another, all units in the repo get copied, no matter what filters were supplied.

The bug is here: https://github.com/pulp/pulp_ostree/blob/24729931bc5c49578e9a11c883a0e95409b23c96/plugins/pulp_ostree/plugins/importers/web.py#L141

It should use the iterable of "units" if provided.

How to reproduce:

pulp-admin ostree repo create --repo-id=f25 --feed=https://kojipkgs.fedoraproject.org/atomic/25/
pulp-admin ostree repo sync run --repo-id=f25
pulp-admin ostree repo search --repo-id=f25

Note that there are two units. I can do a query that matches just one of them:

pulp-admin ostree repo search --repo-id=f25 --str-eq='branch=fedora-atomic/25/x86_64/testing/docker-host'

Now let's create a new repo, and try to copy that one branch using the same filter.

$ pulp-admin ostree repo create --repo-id=f25-test
Repository [f25-test] successfully created

$ pulp-admin ostree repo copy -f f25 -t f25-test --str-eq='branch=fedora-atomic/25/x86_64/testing/docker-host'
This command may be exited via ctrl+c without affecting the request.

[\]
Running...

Copied:
  remote_id:d9680ea424e704ad20d57011c054adb7e3f4ad43f8849c0e1eb9efd4f0ba9bf1
branch:fedora-atomic/25/x86_64/docker-host
commit:27b1ae24686697235c35b793b5c8ab0822b8427e892d3659f0cb300c400979fa
  remote_id:d9680ea424e704ad20d57011c054adb7e3f4ad43f8849c0e1eb9efd4f0ba9bf1
branch:fedora-atomic/25/x86_64/testing/docker-host
commit:35c51948ffdc01c7f235796efcd2b34c7d14b3f1feb417a2ce849ecf2ec13bb2

Notice that it copied both branches. It should have only copied the one matching the filter.