Fetch artifacts from child runs of matrix builds
Add label matching for matrix build runs
Set the default label value to ICE=3.5
Trap HTTPError when fetching CI XML
Discard empty labels
Log an ERROR if incorrect number of matching matrix runs found
--dry-run only stops the final download stage

This means its possible to get a better idea of what would happen
Test upgrade to a matrix build
Fix error when destination config.xml doesn't exist.

AFAICT the only reason this previously worked was that calling omero.cli.CLI() or self.cli.loadplugins() in Upgrade.setup_script_environment() auto-creates a default config.xml (see comment in Upgrade.__init__()).

Why has it broken now? No idea... maybe it's to do with importing multiple versions of the CLI in the nose test harness. Previously only one server was being upgraded in the test run.... perhaps when importing the CLI for the second time it isn't properly imported?
Fix line length
Merge pull request #26 from manics/artifacts_matrix

Add support for downloading artifacts from matrix builds