TestStartTerminationWorker fails on gccgo

[Martin Packman]

New TestStartTerminationWorker fails on ppc64 in CI as the error string is differently cased.

FAIL: machine_test.go:2194: com_juju_juju_cmd_jujud_agent.TestStartTerminationWorker.pN65_github.com_juju_juju_cmd_jujud_agent.machineAgentTerminationSuite

[LOG] 0:00.015 DEBUG juju.cmd.jujud uninstall file "data-dir/uninstall-agent" does not exist
machine_test.go:2209:
    c.Assert(errorFunction(), jc.DeepEquals, &cmdutil.FatalError{
        `"aborted" signal received`,
    })
... obtained *util.FatalError = &util.FatalError{Err:"\"Aborted\" signal received"} ("\"Aborted\" signal received")
... expected *util.FatalError = &util.FatalError{Err:"\"aborted\" signal received"} ("\"aborted\" signal received")
... mismatch at (*).Err: unequal; obtained "\"Aborted\" signal received"; expected "\"aborted\" signal received"

This was introduced by the fix for bug 1464304, landed on master and 1.25:

https://github.com/juju/juju/pull/3536
https://github.com/juju/juju/pull/3538

[Martin Packman (gz)]

Simple fix, accept either casing.

1.25: https://github.com/juju/juju/pull/3541
master: https://github.com/juju/juju/pull/3542