Mutagen sync command indefinite wait fix

[Lunaetic]

Check the output of 'mutagen sync list' for errors, and exit sync command if found, instead of indefinitely waiting.

[navarr]

There must be a way to grab this last error, right?

[Lunaetic]

I'll take a look at capturing the error line and grepping over it, thanks.

[Lunaetic]

Forgot to leave testing steps originally. Can be tested by creating a symlink in the sync'd directory with a target outside the sync'd directory and calling warden sync start. It should exit and output the last mutagen error encountered, instead of waiting indefinitely.

[davidalger]

@Lunaetic Thank you very much for this valuable contribution. Ran a couple tests and it LG2M

$ ln -fsn /tmp/fail webroot/test-fail 
$ warden sync start
Created session sync_zVzJdP7maYOlYUiPJn7xJH2lpeT6jeoJXN2V3cBLzgg                
Waiting for initial synchronization to complete
......
Mutagen encountered an error during sync: alpha scan error: invalid symbolic link (test-fail): target is absolute
$ rm webroot/test-fail 
$ warden sync start
Created session sync_WTh17qqQeP7XVh83MoPaoo1kvZsO05N6iy4OiVjmwp9                
Waiting for initial synchronization to complete
...................
$ 

• Successfully completes under "normal" conditions — pass
• Exits with error message from Mutagen on failure — pass