Driver openzlib rhel6 support - part 2, the last

This is the proper way for RHEL6 / CentOS6 vSwap support which is backward compatible (works correctly on RHEL5 with user_beancounters and on RHEL6 with user_beancounters (without vSwap support switch on))
This pull request contain Andras commits adjusted to current lxcenter/dev branch code