Description of problem:
If I try to sign a tree with the command rpm-ostree compose tree --params..., it will fail because it tries to create a 

Version-Release number of selected component (if applicable):
2015.3 (Fedora 22)


How reproducible:
This is my usage:
# rpm-ostree compose sign --repo=repo --rev=centos-atomic-egym/7/x86_64/standard --key=AAAAA
error: Failed to execute child process "rpm-sign" (No such file or directory)

Then just for testing, I create a link from the file /bin/rpmsign to /bin/rpm-sign and when I try again, having the error:
rpm-sign: --key: unknown option
error: Child process exited with code 1

Which indicates rpmsign is not the command expected to be called by rpm-ostree. I could not find the rpm-sign executable in none of the available packages.

Steps to Reproduce:
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Actual results:
error: Failed to execute child process "rpm-sign" (No such file or directory)

Expected results:


Additional info: