Added support for PV grow

Storage role requires support for a case when PV has to be resized to
fill all available space when its device's size changes (usually on VM).

A new flag 'grow_to_fill' was added, which marks the device for size
expansion (all available space it taken).
Proper size is determined by LVM, avoiding inaccurate size
calculations in blivet.

blivet/formats/lvmpv.py

@@ -99,6 +99,9 @@ def __init__(self, **kwargs):
 
         self.inconsistent_vg = False
 
+        # when set to True, blivet will try to resize the PV to fill all available space
+        self.grow_to_fill = False
+
     def __repr__(self):
         s = DeviceFormat.__repr__(self)
         s += ("  vg_name = %(vg_name)s  vg_uuid = %(vg_uuid)s"

blivet/tasks/pvtask.py

@@ -82,6 +82,11 @@ def __init__(self, a_pv):
     def do_task(self):  # pylint: disable=arguments-differ
         """ Resizes the LVMPV format. """
         try:
-            blockdev.lvm.pvresize(self.pv.device, self.pv.target_size.convert_to(self.unit))
+            if self.pv.grow_to_fill:
+                # resize PV to fill all available space on device by omitting
+                # the size parameter
+                blockdev.lvm.pvresize(self.pv.device)
+            else:
+                blockdev.lvm.pvresize(self.pv.device, self.pv.target_size.convert_to(self.unit))
         except blockdev.LVMError as e:
             raise PhysicalVolumeError(e)