Updated packaging for CentOS 7

Includes systemd service files along with systemd compatible changes for tmpfiles and sysconfig.
A lot of the init helper functions, such as SHMALL and SHMMAX were moved to asd-systemd-helper that is run before the user is changed to aerospike and the server is started.

Has been tested to work with CentOS7 for both building, installing, and running the server after. I also tested a build/install/run with CentOS6 to make sure this did not break anything that was previously working.

However, this was not tested with any of the different malloc implementations and the special logic for each of those.