Run the GEOPM service as an unprivileged user

[dannosliwcd]

This is a hard-coded prototype demonstrating what code needs to be touched (not a proposal for actual changes to be made) if we want to optionally run geopmd as a regular user, which may simplify some testing workflows.

Summary of key changes is:

• We need to be able to customize our /etc and /run paths (either at build time, or at run time should be fine)
• We need to be able to select between system dbus and session dbus
• There are several "am I privileged" checks in the code. Some of those are truly intended as privilege checks, but some of them are "am I a client or am I the service" checks. Those need to be separated out. This draft makes a guess, but I'm not sure if I got it completely right.

Usage:

• Configure with something to put the GEOPM config path on a user-writable location GEOPM_CONFIG_PATH=/tmp/etcgeopm ./configure ...
• On a compute node, stop any actual instances of the geopm service system stop geopm
• On the compute node, start a dbus session: dbus-launch. Note the env vars it prints out.
• Export the env vars printed by dbus-launch. These need to be exported where you run the service, as well as where you run any clients (e.g., geopmread)
• Run geopmd as GEOPM_IS_SERVICE=1 geopmd
• Run geopm clients as normal