Relax dependency on vcloud-tools-tester

So that we can use any version in the 0.1.x series. Necessary to exit
from the current dependency lockstep we're in.
Depend on vCloud Core 0.6.0; release new version

Bump the dependency on vCloud Core 0.6.0 to avoid dependency issues.
Merge pull request #96 from gds-operations/bump-core-version

[#74382904] Depend on vCloud Core 0.6.0; release new version