kpatch: prevent installing a duplicate patch module
kpatch: uninstall should only look in user-installed dir
kpatch: get rid of system-installed modules

The user-installed vs system-installed dichotomy is confusing.  Let's
just have "installed".  RPM-installed modules can just call "kpatch
install" in their post-install step.
kpatch: change --kver to --kernel-version
Merge pull request #199 from jpoimboe/kpatch-install-refactor

kpatch: get rid of system-installed modules