[debian8] add apt-get upgrade to keep in sync with debian testing
[debian8] add workaround needed for up to oar-2.5.4~rc5-1
[debian8] remove workarounds: bug fixed in 2.5.4~rc7-1
[debian8] remove double apt-get update
[kameleon] rename centos6.5 -> centos6
[debian8] add OAR_APT_OPTS to OAR apt-get commands
[centos6] rename vagrant base box -> centos6