How to reproduce:

Clean mock chroot:
{{{
mock -r fedora-review clean
}}}

Run F-R:
{{{
../FedoraReview/try-fedora-review --verbose --prebuilt --rpm-spec --name guava --mock-config fedora-review
}}}

Results:
{{{
Rpmlint (installed packages)

INFO: mock.py version 1.1.21 starting...
State Changed: init plugins
INFO: selinux enabled
State Changed: start
Mock Version: 1.1.21
INFO: Mock Version: 1.1.21
State Changed: lock buildroot
INFO: installing package(s): rpmlint
ERROR: Command failed:
# ['/usr/bin/yum', '--installroot', '/var/lib/mock/fedora-review/root/', 'install', 'rpmlint', '--setopt=tsflags=nocontexts']
Loaded plugins: langpacks, presto, refresh-packagekit
http://download.lab.bos.redhat.com/rel-eng/dist-git/fedora/%24releasever/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found : h\
ttp://download.lab.bos.redhat.com/rel-eng/dist-git/fedora/$releasever/repodata/repomd.xml
Trying other mirror.
Error: Error importing repomd.xml from fedora: Unable to open /var/lib/mock/fedora-review/root/var/cache/yum/x86_64/$releasever/fedora/\
repomd.xml
Could not parse metalink https://mirrors.fedoraproject.org/metalink?repo=fedora-$releasever&arch=x86_64 error was
No repomd file
Could not parse metalink https://mirrors.fedoraproject.org/metalink?repo=updates-released-f$releasever&arch=x86_64 error was
No repomd file
}}}