added Atmo prefix to User model class name
Merge pull request #20 from dice-cyfronet/strange_user_fund_fix

added Atmo prefix to User model class name
do nothing when VM is already deleted

VM tagging is invoked with some delay (when VM should be already seen by
cloud REST API). As a conclusion there can be a situation when VM tagging
is invoked by user already removed selected VM.

Fixes #23
Merge pull request #24 from dice-cyfronet/tags

do nothing when VM is already deleted