core: resolve specifier in config_parse_exec()

When parse ExecXXX=, specifiers are not resolved in
config_parse_exec(). Finally, the specifiers are set into unit
properties. So, systemctl shows not resolved speicifier on "Process:"
field.
To set the exec properties well, resolve specifiers before parse the
rvale by unit_full_printf();

src/core/load-fragment.c

@@ -574,7 +574,9 @@ int config_parse_exec(
                 void *data,
                 void *userdata) {
 
+        _cleanup_free_ char *cmd = NULL;
         ExecCommand **e = data;
+        Unit *u = userdata;
         const char *p;
         bool semicolon;
         int r;
@@ -583,6 +585,7 @@ int config_parse_exec(
         assert(lvalue);
         assert(rvalue);
         assert(e);
+        assert(u);
 
         e += ltype;
         rvalue += strspn(rvalue, WHITESPACE);
@@ -593,7 +596,13 @@ int config_parse_exec(
                 return 0;
         }
 
-        p = rvalue;
+        r = unit_full_printf(u, rvalue, &cmd);
+        if (r < 0) {
+                log_syntax(unit, LOG_ERR, filename, line, r, "Failed to resolve unit specifiers on %s, ignoring: %m", rvalue);
+                return 0;
+        }
+
+        p = cmd;
         do {
                 _cleanup_free_ char *path = NULL, *firstword = NULL;
                 bool separate_argv0 = false, ignore = false;