CLI download looks for resources in all user groups (fix #12146).

[bpindelski]

This PR updates the logic used by bin\omero download. Now all groups in which the logged in user is present are used when looking for an Image / OriginalFile / FileAnnotation ID. To test, follow scenario from http://trac.openmicroscopy.org.uk/ome/ticket/12146. Try out downloading an Image, FileAnnotation and OriginalFile.

\cc @joshmoore, @sbesson: I'd appreciate feedback with regards to code and test structure - happy to correct if there is too much copypasta.

[joshmoore]

$ bin/omero login root@localhost
$ bin/omero group add d1
Added group d1 (id=1503) with permissions rw----
$ bin/omero group add d2
Current group: system
Added group d2 (id=1504) with permissions rw----
$ bin/omero user add d Download Tester d1 d2
Please enter password for your new user (d): 
Please re-enter password for your new user (d): 
Added user d (id=1502) with password
$ bin/omero login d@localhost
Created session 9e849318-a590-4be3-bcbf-0aa0c4f1caad (d@localhost:4064). Idle timeout: 10.0 min. Current group: d1
$ bin/omero upload etc/omero.properties                                                                                                                    
Uploaded etc/omero.properties as 753
$ bin/omero download 753 - | grep omero.version                                                                                    
omero.version=5.0.1-DEV-ice35
$ bin/omero sessions group 1504
Group 'd1' (id=1503) switched to 'd2' (id=1504)
$ bin/omero download 753 - | grep omero.version
omero.version=5.0.1-DEV-ice35

Works great. @bpindelski : my proposed refactoring to getContext() is available in 4dc88e7

[bpindelski]

@joshmoore Thanks. You beat me to it - I was just about to push almost the same-looking code. Will cherry-pick.

[sbesson]

Won't have time to make an extensive review of it but 👍 from my side by looking at it.

[joshmoore]

@joshmoore Thanks. You beat me to it - I was just about to push almost the same-looking code. Will cherry-pick.

Doh, sorry. Had it built locally for testing and figured might as well.

[bpindelski]

Would this benefit from waiting on @sbesson's review?

[joshmoore]

With @sbesson away, let's let him open a PR if he'd like to refactor your tests! 😄 I think with our 4 (6) eyes having been on it, we should be good to go. Merging. If anyone of the PY gateway contributors want to propose expanding the scope of the getContext() method, they need just say so. /cc @will-moore @knabar @aleksandra-tarkowska @cneves

[bpindelski]

--rebased-to #2398