Mdadm provider fails to load current resource if the system contains an unrelated inactive array

`mdadm --detail --scan` returns a nonzero exit status when it detects an
inactive RAID array. Since the mdadm provider invokes this with the
`shell_out!` method, load_current_resource fails (regardless of current
resource status) if any inactive array is present in the system:

[Wed, 01 Aug 2012 04:07:40 +0000] FATAL: Mixlib::ShellOut::ShellCommandFailed: mdadm[/dev/md0] (mysql::percona_server line 22) had an error: Mixlib::ShellOut::ShellCommandFailed: Expected process to exit with [0], but received '1'

In this case an inactive /dev/md1 was blocking my configuration of /dev/md0.