If ironic-python-agent is not installed in the IPA image using
upper-constraints, the ironic-lib selected by pip for installation may
be newer than ipa.
Use upper-constraints for the same version as ironic-python-agent when
installing it, by passing the DIB_REPOREF_requirements environment
variable to ironic-python-agent-builder.
Closes-Bug: #2089263
Change-Id: I6e33f9897dc7efc57987872ffccdfbe0fc78cc52
89849c1cec