anaconda: lower disk requirements

Base installed system, including one template uses about 8GB. So make it
possible to install the system with root partition about that size. This
is probably bad idea, but the limit here is hard - it isn't possible to
force installation on smaller partition.

anaconda/pyanaconda/installclasses/qubes.py

@@ -67,7 +67,7 @@ class InstallClass(BaseInstallClass):
         for autoreq in storage.autoPartitionRequests:
             if autoreq.mountpoint == "/":
                 autoreq.maxSize=None
-                autoreq.requiredSpace=24*1024
+                autoreq.requiredSpace=10*1024
             if autoreq.mountpoint == "/home":
                 storage.autoPartitionRequests.remove(autoreq)