Fix #529 1 "This Session's transaction has been rolled back"

[LAlbertalli]

Fix one of the issues found in #529

Background:

• When an object is modified by SQLAlchemy, it is invalidated so need to be fetched again from the DB
• If there's an exception during a transaction, SQLAlchemy performs a rollback and mark the connection as dirty.

Bug:

• When handling exceptions, the exception handler tries to access the name of the cluster in the main object. Since the name has been invalidated due to a write, SQLAlchemy tries to fetch it on a 'dirty' connection and spits out an error.
  Solution:
• Fetch the information for handling the exception before starting the process.

[landscape-bot]

Repository health decreased by 0.03% when pulling 072a09e on LAlbertalli:fix529-1 into 7d27692 on airbnb:master.

• 1 new problem was found (including 0 errors and 0 code smells).
• No problems were fixed.

[coveralls]

Coverage decreased (-0.06%) to 82.108% when pulling 072a09ec88ce7991de228d75a80f191f07ca16c3 on LAlbertalli:fix529-1 into 7d27692 on airbnb:master.

[xrmx]

@LAlbertalli it would be cool to have all the description you write in pull requests in the git commit messages too :)

[LAlbertalli]

@xrmx Git Amended the commit message to insert the description of the error

[coveralls]

Coverage decreased (-0.06%) to 82.108% when pulling 4e98617 on LAlbertalli:fix529-1 into 7d27692 on airbnb:master.

[mistercrunch]