Fix finding bridge slaves

Commit f2f444ab broke the detection of bridge slaves: it tried to check
if symlinks were pointing to existing files, but was not expanding the
paths to absolute paths. So the tests were failing because they were
done on relative paths...

Commit cb6c1b84 attempted to fix that, but the fix wasn't fully correct
either as far as I can tell: it does
File.join("/sys/class/net/foo/brif/eth0.300", "../../eth0.300/brport")
instead of
File.join("/sys/class/net/foo/brif", "../../eth0.300/brport")

Note that we're using File.expand_path (and not File.realpath) to keep
compatibility with ruby 1.8.x.
Add a minimal OvsBridge Class

This fixes crash in Nic::destroy() when calling it for an openvswitch bridge.
It only implements the barely minimum to make Nic::destroy work.  (Fixes:
bnc#846821)
Integrated bootstrap templating
Do not consider cinder volumes as local disks

They belong to the VMs really, so don't add them to the fixed/unclaimed
disks list. Fixes bnc#826569
Merge pull request #164 from vuntz/fix-bridge-slaves-roxy

Fix finding bridge slaves
Merge pull request #171 from tboerger/feature/bootstrap

+1
Merge pull request #168 from rhafer/fix/bnc846821

Add a minimal OvsBridge Class
Add webui for useful attributes

The only which I think is really useful is use_allocate.
Merge pull request #174 from vuntz/webui

Add webui for useful attributes
Call super method in *Service.initialize
Merge pull request #175 from vuntz/validation

Call super method in *Service.initialize
Merge pull request #172 from dirkmueller/release/roxy/master

Do not consider cinder volumes as local disks
Also add Support for Xen Virtual Disks (/dev/xvd*)
Merge pull request #178 from dirkmueller/release/roxy/master

Also add Support for Xen Virtual Disks (/dev/xvd*)
Drop executable bits on files
Merge pull request #179 from vuntz/no+x

Drop executable bits on files
Replace rm known_hosts with rm -f
Merge pull request #182 from tboerger/feature/rm-silence

Replace rm known_hosts with rm -f