Fix the order of exceptions in Lock.aquire

The error: Lock.acquire: Bad except clauses order (KazooException is an ancestor class of RetryFailedError) was reported by pylint. The RetryFailedError path would never be executed, leading to a wrong flag set in case of cancelation, for example.
Remove extra line inserted in the previous commit.
Merge pull request #146 from ReneSac/master

Fix the order of exceptions in Lock.aquire