Update electron statuses for `AWSEC2Executor`

[kessler-frost]

Once separation of workflow and electron statuses is done, the electron level statuses need to be updated to accommodate executor dependent statuses. In this case the following status definitions will be updated:

• PROVISIONING - Instance is being provisioned

• REGISTERING - Connection established to the remote machine and files are being transferred

• RUNNING - Execution invoked on the remote machine

• COMPLETING - Results files being retrieved, temporary files are being deleted, and the connection is being closed

• DEPROVISIONING - Instance is being deprovisioned

For the end state, there is a separate class called EndState and contains all possible end state statuses like COMPLETED, FAILED, etc. and thus does not need to be added to the executor dependent status.

Acceptance Criteria:

• Above mentioned statuses need to be updated inside the local executor
• Tests need to be added to verify if those definitions are as expected