Add cross-account support to mjob. Fix mjob cost when the Manta job has errors.

Support cross-account mjob queries by specifying the full path:
mjob get /:login/jobs/:id.
Also improved mjob cost so that the job's output will print even if the job has
errors, which happens sometimes when a job is created and input keys aren't
added until later.
Merge pull request #135 from fkuo/xacctmjob

Add x-account support to mjob. Fix mjob cost when the Manta job has errors.