Bug: getByName exception should not be unknown

[joshmoore]

see: https://www.openmicroscopy.org/qa2/qa/feedback/29734/

A database busy exception thrown during service loading led to an Ice.UnknownException whereas this should be a retry-able exception:

java.lang.Exception: omero.gateway.exception.DSAccessException: Cannot access data. 
Cannot find split images.
    at org.openmicroscopy.shoola.env.data.OMEROGateway.handleException(OMEROGateway.java:771)
    at org.openmicroscopy.shoola.env.data.OMEROGateway.getImagesBySplitFilesets(OMEROGateway.java:7527)
    at org.openmicroscopy.shoola.env.data.OmeroDataServiceImpl.getImagesBySplitFilesets(OmeroDataServiceImpl.java:1101)
    at org.openmicroscopy.shoola.env.data.views.calls.ImageSplitChecker$1.doCall(ImageSplitChecker.java:156)
    at org.openmicroscopy.shoola.env.data.views.BatchCall.doStep(BatchCall.java:144)
    at org.openmicroscopy.shoola.util.concur.tasks.CompositeTask.doStep(CompositeTask.java:226)
    at org.openmicroscopy.shoola.env.data.views.CompositeBatchCall.doStep(CompositeBatchCall.java:126)
    at org.openmicroscopy.shoola.util.concur.tasks.ExecCommand.exec(ExecCommand.java:165)
    at org.openmicroscopy.shoola.util.concur.tasks.ExecCommand.run(ExecCommand.java:276)
    at org.openmicroscopy.shoola.util.concur.tasks.AsyncProcessor$Runner.run(AsyncProcessor.java:91)
    at java.lang.Thread.run(Thread.java:745)
Caused by: omero.gateway.exception.DSOutOfServiceException: Could not load omero.api.IContainer
    at omero.gateway.Connector.get(Connector.java:1038)
    at omero.gateway.Connector.getPojosService(Connector.java:350)
    at omero.gateway.Gateway.getPojosService(Gateway.java:702)
    at org.openmicroscopy.shoola.env.data.OMEROGateway.getImagesBySplitFilesets(OMEROGateway.java:7522)
    ... 9 more
Caused by: Ice.UnknownException
    unknown = "ome.conditions.DatabaseBusyException: cannot create transaction