More safely install/uninstall with weak-modules

This addresses some minor issues with how we handle driving the
weak-modules infrastructure for handling running on kernels not
explicitly built for.

For one, we now drive weak-modules at install-time more explicitly (it
was adding symlinks for all modules into the right place for the running
kernel, whereas now it only handles that for scoutfs against all
installed kernels).

Also we no longer leave stale modules on the filesystem after an
uninstall/upgrade, similar to what's done for vsm's kmods right now.
RPM's pre/postinstall scriptlets are used to drive weak-modules to clean
things up.

Note that this (intentionally) does not (re)generate initrds of any
kind.

Finally, this was tested on both the native kernel version and on
updates that would need the migrated modules. As a result, installs are
a little quicker, the module still gets migrated successfully, and
uninstalls correctly remove (only) the packaged module.

kmod/scoutfs-kmod.spec.in

@@ -97,10 +97,21 @@ find %{buildroot} -type f -name \*.ko -exec %{__chmod} u+x \{\} \;
 /lib/modules
 
 %post
-weak-modules --add-kernel --no-initramfs
+echo /lib/modules/%{kversion}/%{install_mod_dir}/scoutfs.ko | weak-modules --add-modules --no-initramfs
 depmod -a
 %endif
 
 %clean
 rm -rf %{buildroot}
 
+%preun
+# stash our modules for postun cleanup
+SCOUTFS_RPM_NAME=$(rpm -q %{name} | grep "%{version}-%{release}")
+rpm -ql $SCOUTFS_RPM_NAME | grep '\.ko$' > /var/run/%{name}-modules-%{version}-%{release} || true
+
+%postun
+if [ -x /sbin/weak-modules ]; then
+    cat /var/run/%{name}-modules-%{version}-%{release} | /sbin/weak-modules --remove-modules --no-initramfs
+fi
+
+rm /var/run/%{name}-modules-%{version}-%{release} || true