Fix installation of old package instead of SNAPSHOT one

Steps to reproduce:
(distribution taken from
https://qa.nuxeo.org/jenkins/job/nuxeo-master-fullbuild-permanentCheck/3184/ against connect-test deployed with https://qapriv.nuxeo.org/jenkins/job/nuxeo-connect-master/batchTasks/task/Deploy%20to%20Connect%20Test/706-1/)

• i'm testing with my sandbox atchertchian-SANDBOX, it has an old MP that was tagged on 5.6, and is currently set to use 5.8 target platform without packages
• i install a nuxeo, after nuxeoctl init to initialize local packages
• i register, and update my studio project once using the "update snapshot" button, it is indeed installed
• on studio side, i decide to add the DM package
• on Nuxeo side, i update the studio project using the "update snapshot" button, and i have a validation error saying i'm missing DM, so i hit "cancel"
• so i install DM, from the UI or using nuxeoctl (same issue in both cases, printing output logs herewhen using nuxeoctl):

$ ./bin/nuxeoctl mp-install nuxeo-dm
Detected Tomcat server.
Nuxeo home:          /opt/nuxeo-cap-5.8-SNAPSHOT-tomcat
Nuxeo configuration: /opt/nuxeo-cap-5.8-SNAPSHOT-tomcat/bin/nuxeo.conf
Include template: /opt/nuxeo-cap-5.8-SNAPSHOT-tomcat/templates/common-base
Include template: /opt/nuxeo-cap-5.8-SNAPSHOT-tomcat/templates/common
Include template: /opt/nuxeo-cap-5.8-SNAPSHOT-tomcat/templates/default

Dependency resolution:
  Installation order: nuxeo-dm-5.8.0-SNAPSHOT/atchertchian-SANDBOX-0.0.1-testMP
  Packages to upgrade: atchertchian-SANDBOX:0.0.0-SNAPSHOT

Do you want to continue (yes/no)? [yes] yes
Downloading [atchertchian-SANDBOX-0.0.1-testMP]...
Added atchertchian-SANDBOX-0.0.1-testMP
Uninstalling atchertchian-SANDBOX-0.0.0-SNAPSHOT
Installing nuxeo-dm-5.8.0-SNAPSHOT
Installing atchertchian-SANDBOX-0.0.1-testMP

-> if i start, the testMP package is visible instead of the SNAPSHOT one, and it's been configured for a 5.6 (the package.xml file references only cap-5.6 target platforms and the nuxeo-dm package as a dependency, could this be fixed or avoided by changing the corresponding min version?)

Problem was not visible on 5.7.3, because to perform validation, Studio downloaded the new package, and uninstalled it. This led to other issues like this one (random) NXP-12121, that is now fixed with changes for NXP-9343.

I had another problem when playing with the DAM package also, i got in a situation where i could not uninstall neither my sandbox nor dam (but i haven't tried to reproduce this one for now)