Speed up finding of default_platform

Rather than listing all nodes, simply search
for the admin node.
Remove node.save during webui list operations

listing of all nodes or unallocated nodes caused node.save
operations on all nodes, which can cause races.
apache2: Fix the status.conf template for SUSE

We need to explicitly allow 127.0.0.1, as localhost resolves to IPv6.
Merge pull request #1050 from vuntz/merge-roxy

apache2: Fix the status.conf template for SUSE
Merge pull request #1047 from dirkmueller/default_platform

Default platform
Node target_platform fallbacks to default_platform

The default platform of the nodes is inferred from the platform of the
admin node (and is empty if there's no admin node - possible bug?)

Move the default_platform helper code to NodeObject class, where it gets
cached.

Then use it in the target_platform as a fallback.