swift-recon-cron: do not get confused by files in /srv/node
swift-recon-cron: do not get confused by files in /srv/node

swift-recon-cron looks at the drives mounted in directories below
/srv/node, but before this commit, it tried to call listdir() on
everything in this directory, even if it is not a directory.

Change-Id: Id281352f7ab6ecb520eb00f3649873d8c8678608
Signed-off-by: Stefan Majewsky <23888fbbf34aeec099df058e607cbf00c99a1b6b@sap.com>

matthewoliver/swift,tipabu/swift,smerritt/swift,swiftstack/swift,smerritt/swift,smerritt/swift,openstack/swift,swiftstack/swift,matthewoliver/swift,openstack/swift,tipabu/swift,openstack/swift,tipabu/swift,smerritt/swift,swiftstack/swift,matthewoliver/swift,openstack/swift,matthewoliver/swift,tipabu/swift