Description of problem:
"mock install" cannot install any local RPMs.

Version-Release number of selected component (if applicable):
mock-1.4.1-1.fc25.noarch

How reproducible:
always

Steps to Reproduce:
1. Locally download an .rpm file, for example:
dnf download kernel-core-4.10.16-200.fc25.x86_64
2. mock -r fedora-25-x86_64 init
3. mock -r fedora-25-x86_64 install kernel-core-4.10.16-200.fc25.x86_64.rpm

Actual results:
Mock fails with an error

Expected results:
Mock installs the package into the F25 chroot.

The above steps work fine with mock-1.3.4-1.fc25. It occurs for any .rpm I tested, not just kernel-core.

Additional info:
Here is the output from "mock install" with the local .rpm file:
...
Mock Version: 1.4.1
INFO: Mock Version: 1.4.1
Finish: chroot init
INFO: installing package(s): kernel-core-4.10.16-200.fc25.x86_64.rpm
Can not load RPM file: kernel-core-4.10.16-200.fc25.x86_64.rpm.
ERROR: Command failed: 
 # /usr/bin/systemd-nspawn -q -M 88adba6792264b0c9ba044cf6f87219b -D /var/lib/mock/fedora-25-x86_64-bootstrap/root -a --setenv=LC_MESSAGES=C --setenv=LANG=en_US.utf8 --setenv=PROMPT_COMMAND=printf "\033]0;<mock-chroot>\007" --setenv=SHELL=/bin/bash --setenv=PATH=/usr/bin:/bin:/usr/sbin:/sbin --setenv=PS1=<mock-chroot> \s-\v\$  --setenv=HOME=/builddir --setenv=HOSTNAME=mock --setenv=TERM=vt100 /usr/bin/dnf --installroot /var/lib/mock/fedora-25-x86_64/root/ --releasever 25 --disableplugin=local --setopt=deltarpm=false install kernel-core-4.10.16-200.fc25.x86_64.rpm