by-path links for virtio disk might not exist

Newer udev releases don't create the by-path links anymore for virtio disks.
Don't try to resolve to "by-path" links for virtio devices for any platform
that is newer than what we currenlty support (e.g. SLE-12). Use the /dev/vdX
names in that case instead.
Merge pull request #1129 from rhafer/sle-12-virtio

by-path links for virtio disk might not exist
cleanup unused variables

- turn is_admin into a helper and use that instead
- level :info is the default log level
Merge pull request #1132 from mapleoin/cleanup

cleanup unused variables
Fix typo in variable name

undefined local variable or method `virtio_by_path_platform'
Merge pull request #1133 from dirkmueller/syntax_error_fix

Fix typo in variable name
Lib: Make cluster methods callable on ServiceObject class
Lib: Do not cache available_clusters

Displaying the clusters menu item would break if the pacemaker proposal
is deactivated.
Lib: Add a helper method for determining cluster status
UI: Allow skipping reloads on status/page discrepancy
UI: Move glyphicon styles up so they work in dashboard too
Models: Helper methods for cluster and proposal lookups

Methods for fetching the nodes and roles associated with the given
cluster (pacemaker role) or proposal.
Models: Make sure RoleObject#elements always returns a hash
Models: Helper methods for active roles page

Methods that allow to look up nodes or clusters associated to a role,
and query various role's properties (assigned, HA, proposal).

It also introduces a concept of a 'core role', which is a role deployed
by default on a newly allocated node.
Routing: Add routes pointing to new dashboard
Controllers: Complete dashboard controller

The dashboard suffers the same problem as every other - large amounts of
data needs to be pulled in. However, with chef (api), the round trip of
one request is up to 30ms, so loading anything repeatedly or fetching
single records is out of the question.

So we do two things:

1) Preload all *Objects. This is inefficient, but still is faster than
fetching individual records or running find_all_by queries.

2) Methods that search for certain kinds of *Objects or fetch associated
records of an *Object accept an array of unfiltered values retrieved in
1), then operate on that, rather then querying on their own.
Views: Add clusters and active role views
i18n: Translation strings for cluster/role dashboards
Nav: add menu links to cluster / roles dashboard
Fix lowercase in active roles title