commands: move constant attr_postfix = "_old" into rocks.db.helper
tests: no space in the temporary directory used during tests

The temporary directory used during the tests had a space
and this was causing problem with rocks create distro (which does
not support space)
rocks: now the self.db.database is never null

it alwys points to a valid instance of rocks.db.database.helper.database
class. This is necessary to make commands work without database
connection
pylib: db.database.database.Database now works also without a connection

the class can be instantiated and work properly even if the connection
to the db is not up
tests: rocks command that must work without the DB connection

This test suite runs all the commands that should be able to run
without a DB connection (used during FE installation or at bootstrap)