Fix CMake install absolute path to support --prefix option

[x12301450]

In your CMakeLists.txt, five absolute path are used as the destination of install command, which is not recommended by CMake.

agent/CMakeLists.txt: 89 and 100

SET(SYS_CONFIG_DIR ${CMAKE_INSTALL_FULL_SYSCONFDIR}/softwarecontainer/)
install(FILES "${CMAKE_CURRENT_BINARY_DIR}/softwarecontainer-config" DESTINATION ${SYS_CONFIG_DIR})

install(FILES softwarecontainer-agent.conf DESTINATION "/etc/dbus-1/system.d")

examples/temperature/temperature-service/CMakeLists.txt: 27

install(FILES ${CMAKE_CURRENT_SOURCE_DIR}/dbus/com.pelagicore.TemperatureService.conf
            DESTINATION /etc/dbus-1/system.d/)

libsoftwarecontainer/CMakeLists.txt: 57 and 59

install(FILES ${CMAKE_CURRENT_BINARY_DIR}/softwarecontainer.pc DESTINATION ${CMAKE_INSTALL_FULL_LIBDIR}/pkgconfig)

install(FILES ${CMAKE_CURRENT_BINARY_DIR}/softwarecontainer.conf DESTINATION ${SYS_CONFIG_DIR})

When attempting to use the --prefix option to relocate the installation destination, using an absolute path causes the installation to fail. This prevents the installation to custom prefixes and could lead to unintended issues.

There are numerous similar fixes, such as this example.

I think the destinatioin should be set to a relative path, excluding ${CMAKE_INSTALL_PREFIX}. For example, using CMAKE_INSTALL_SYSCONFDIR rather than full_dir would be a better practice.

[tobsan]

Surely you must be aware by now, that this project is mostly dead? Afaik, the OSS effort has been pretty much abandoned, and the only actual users forked it into their own walled garden.