Added CentOS install functionality.

install_packages, remove_packages, and remove_sources are now the installation
fuctions used by teuthology.  Debian references have been removed outside of
tasks/install.py.  CentOS functionality parallel to Debian has been added to
tasks/install.py.

System types are used as keys to distiguish between Ubuntu and Centos.
Changes were also made to make -a option work for Centos (use service
to restart rsyslog, and make sure all directories exist when copying
log files).

In order to get ceph to run, several sections of the ceph task,
ceph_manager task, clock, and internal task are run as super user.  Also, files
created while running Centos are currently deleted with 'rm -fr'
(rather than using an rpm based method).

Signed-off-by: Warren Usui <warren.usui@inktank.com>