Moved v2 tests for plugins to new location
Adding block code and tests
Update block.py

Add note on block properties
Preserve backup files

This commit introduce two distinct changes:

- an existing backup file is never overwritten;
- the backup extension is the same for all backups in a given run.

Without this commit if a file is modified multiple times in the same
play only the last edit can be rolled back.

Signed-off-by: Walter Franzini <walter.franzini@gmail.com>