Initialize shares variables for RemoteFsDriver(s)

self.shares and self._mounted_shares are used by various methods
for RemoteFs-based drivers, but may not be instantiated early enough.

Initialize them in __init__ to ensure they always exist.  (Also fixes
pylint warnings.)

Closes-Bug: #1239741
Change-Id: I0ef884c28b82b7f694cf8a0fb4629c835da11c91

cinder/volume/drivers/nfs.py

@@ -73,6 +73,8 @@ class RemoteFsDriver(driver.VolumeDriver):
 
     def __init__(self, *args, **kwargs):
         super(RemoteFsDriver, self).__init__(*args, **kwargs)
+        self.shares = {}
+        self._mounted_shares = []
 
     def check_for_setup_error(self):
         """Just to override parent behavior."""