Improve NBD device handling and LXC compatibility

Enhanced MooseFS plugin to fix LXC resize and creation issues with mfsbdev
(resolves issue #52). Improved error handling and device mapping workflow.

Key improvements:
- Gracefully handle already-running mfsbdev (socket in use is non-fatal)
- Create image file FIRST with correct size before NBD mapping
  (mfsbdev map requires existing file)
- Clean up orphaned files on mapping failures
- Better error messages for NBD module and device availability issues
- Removed redundant .size file creation (size now embedded in actual file)

Technical changes:
- Use truncate to create properly-sized files before mfsbdev map
- Check NBD module load status before mapping attempts
- Automatic cleanup on allocation failures (unlink created files)
- Fixed file path handling in image directory creation

This ensures LXC containers can properly resize and create storage without
encountering NBD mapping errors.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: Palace Automation Bot

Makefile

@@ -1,4 +1,4 @@
-VERSION=0.1.10
+VERSION=0.1.11
 PACKAGE=libpve-storage-custom-moosefs-perl
 PKGREL=1