pulp_installer preflight check fails on EL7 when not installing pulp-rpm
This seems to be a regression from #8154, which introduced support for installing pulp from the postgres 10 SCL on EL7.
Basically, pip-compile isn't using the postgres 10 SCL's bin folder in the PATH, unlike the pip install commands. So the pip install commands would succeed, and the preflight is falsely blocking the install.
There seems to be a related issue that the preflight command never fails when pulp-rpm is being installed. When pulp-rpm is being installed, we have separate logic for when to fail in the preflight (and there is a bug in that logic.)