Deal gracefully with locked excel files

[SeanAdams]

Currently - if someone has accidentally kept an excel file open on their desktop, Alteryx will fail to load this flow.

However, it would make more sense to open this file without read-lock as a dirty-read (equivalent of "Read Uncommtted").

This may require some interaction with Microsoft but would be worth pursuing because it prevents / eliminates an entire category of needless canvas errors.

[DanielG]

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