Milestone ProvisioningService: Integrate resource discovery and selection

Raven now supports resource discovery and selection via CoMon queries. In particular, the Pacman tool allows the user to define groups of nodes, and to install packages in slices based on those groups. Pacman now allows groups to be defined based on the results of CoMon queries. The CoMon results can be used to define groups both statically and dynamically. Static group definition is done when the Pacman group file is created by using the result of the query to define the groups in the file. Dynamic group definition is done at run-time by including the query itself in the Pacman group file, so that each node performs the query at run-time and decides on the fly whether or not it is a member of the group. It is anticipated that static queries will be used for resources that do not change rapidly (e.g. the number of CPU cores) whereas dynamic queries will be used for resources that do change rapidly (e.g. the amount of free disk space on the node).