sd-path: rename the two functions

I think the two names were both pretty bad. They did not give a proper hint
what the difference between the two functions is, and sd_path_home sounds like
it is somehow related to /home or home directories or whatever, when in fact
both functions return the same set of paths as either a colon-delimited string
or a strv. "_strv" suffix is used by various functions in sd-bus, so let's
reuse that.

Those functions are not public yet, so let's rename.
diff --git a/src/tmpfiles/tmpfiles.c b/src/tmpfiles/tmpfiles.c
index d1ba584..6ab30cd 100644
--- a/src/tmpfiles/tmpfiles.c
+++ b/src/tmpfiles/tmpfiles.c
@@ -244,7 +244,7 @@
         i = PTR_TO_UINT(data);
         assert(i < ELEMENTSOF(paths_system));
 
-        return sd_path_home(paths[i].type, paths[i].suffix, ret);
+        return sd_path_lookup(paths[i].type, paths[i].suffix, ret);
 }
 
 static int log_unresolvable_specifier(const char *filename, unsigned line) {