remove nexus.version/project.version hacks, which seems not needed anymore

these hacks were added before the glom merge of nexus projects into single repo
Revert "remove nexus.version/project.version hacks, which seems not needed anymore"

This reverts commit c79f7b72be136b9c45bfa0218b5aab4a709e596d.
correct the parent being used

Conflicts:
	plugins/p2/nexus-p2-client/pom.xml
2.6.1-SNAPSHOT
Merge remote-tracking branch 'origin/master' into nexus-5584-conf-writes