libsystemd: new library, refactor sd-daemon.[ch] test code

This commit introduces a bare-bones replacement for libsystemd:

 - Build .so file and add --with-libsystemd to configure
 - Add capabilities support to test/src/serv.c
 - Update tests to account for a Finit built w/o libsystemd support

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

libsystemd/.gitignore

@@ -0,0 +1,7 @@
+.deps/*
+.libs/*
+.dirstamp
+*.lo
+libsystemd.*
+Makefile
+Makefile.in