Fixed wrong package manager command for rhel. ;-)

Additionally we now have the consistent naming convention for CentOS
too:

centos-<maj>.<min>-<platform>[-puppet][-<builder>]
EPEL repo installation now release aware.

Dependent on release version and platform of OS, the correct version of
EPEL is now installed from RPM package.
Improved behavior of scripts regarding verbosity. No functional changes.

Decreased verbosity of most commands but respectively added more
echo statements to know what's going on. No functional changes!
Switch back to curl as wget is not yet installed.
Additional package ntpdate for each template now gets installed.

The package ntpdate is recommended by beaker therefore we ensure it's
installed.