Cross-site phantom checks are not automatic

[shippy]

See for example this SRI scan of a UCSD subject, which looks for a UCSD phantom (#9739):

ncanda@pipeline-back[pipeline_back_1]:/sibis-software/ncanda-data-integration/scripts (master)$ xnat/check_phantom_scans -e NCANDA_E10772
{"experiment_site_id": "E-99999-P-9-06df12", "error": "ERROR: subject could not be found!", "err_msg": "'Could not find ID/label E-99999-P-9 in collection!'", "project": "sri_incoming", "function": "session.xnat_get_subject", "subject": "E-99999-P-9"}
{"experiment_site_id": "E-99999-P-9", "error": "ERROR: session.xnat_get_subject_attribute: subject E-99999-P-9 not found !", "project": "sri_incoming"}
{"experiment_site_id": "NCANDA_E10772", "error": "Could not get phantom id for phantom E-99999-P-9", "project_id": "sri_incoming", "phantom": "E-99999-P-9", "related_issues": [], "cmd": "xnat/check_phantom_scans -e NCANDA_E10772"}

[shippy]

Not actually broken - I'd just forgotten it's addressed via special_cases.yml instead of programmatically. It could be addressed programmatically and that might save us sometyping, though.