composer: Add the yum cache archive size to the size estimate

anaconda moves the yum cache to the disk once it is partitioned, so the
downloaded rpms also consume space until the installation is finished.
Take this into account when estimating the size.

Thanks to Christophe Besson for spotting this.

Related: rhbz#1761337

src/pylorax/api/projects.py

@@ -363,6 +363,8 @@ def estimate_size(packages, block_size=4096):
     for p in packages:
         installed_size += len(p.po.filelist) * block_size
         installed_size += p.po.installedsize
+        # also count the RPM package size (yum cache)
+        installed_size += ((p.po.size / block_size) + 1) * block_size
     return installed_size
 
 def projects_depsolve_with_size(yb, projects, groups, with_core=True):