Add missing storage helper

hooks/charmhelpers/contrib/storage/linux/utils.py

@@ -0,0 +1,25 @@
+from os import stat
+from stat import S_ISBLK
+
+from subprocess import (
+    check_call
+)
+
+
+def is_block_device(path):
+    '''
+    Confirm device at path is a valid block device node.
+
+    :returns: boolean: True if path is a block device, False if not.
+    '''
+    return S_ISBLK(stat(path).st_mode)
+
+
+def zap_disk(block_device):
+    '''
+    Clear a block device of partition table. Relies on sgdisk, which is
+    installed as pat of the 'gdisk' package in Ubuntu.
+
+    :param block_device: str: Full path of block device to clean.
+    '''
+    check_call(['sgdisk', '--zap-all', block_device])