Initial systemdunitproperty and systemdunitdependency object implementation
Temporary build system hacks regarding libdbus
libdbus code to query unit dbus path by systemd unit name
libdbus code to query all properties of a unit by its path

The properties are just outputted using dI for now.
Added work in progress function to retrieve one property value from systemd unit path
Changed signature of get_all_properties_by_unit_path to return exit code
Skip complex dbus properties when querying systemd unit properties
Only query properties from the systemd Unit interface, skip the rest
Fixed single property retrieval in systemdunitproperty probe
Initial dbus array to string support in systemdunitproperty probe
Extracted shared systemd test functionality into systemdshared.h, added a simple test function
Getting all properties is only required in the unit property probe, cleanup
Initial code for systemdunitdependency test, prints transitive deps for given unit
Only recurse into target units in systemdunitdependency probe

Same behavior as systemctl list-dependencies --plain $UNIT
Refactoring to avoid code duplication in systemdunitdependency probe
Initial versions of systemdunit{property,dependency} tests
Renamed systemdunitdependency test data
Renames and minor fixes in systemd probe tests, distcheck passes
Added get_all_systemd_units to the shared systemd tests mini API

This functionality is required for pattern matching across systemd
units.
[probes/systemd API] If not sure, use a callback.