Rework datastore tests

Sysrepo now supports parallelized tests. Use the new environmental
variables to implement this in netconf-cli. All of the tests now get
their own clean environment:

- Fresh repository and separate shm prefix. These get cleaned before and
after tests. The only thing that gets left are some empty directories.

- Its own model to test on.

- Separate Netopeer2 daemon: only for netconf tests - that means no
`sleep 5` for sysrepo-only tests. So no useless waiting. Wow! The daemon
also runs with its argv[0] changed to something recognizable for
`pkill`. That means that if Netopeer2 crashes for some reason, pkill
will notify me.

Side note: These changes somehow changed some of the linking, so hopefully I got
those right.

Change-Id: Ib0e582ef03fc559b24203af8afb2a295a6318ca9
diff --git a/tests/mock/sysrepo_subscription.cpp b/tests/mock/sysrepo_subscription.cpp
index 5527c41..03be075 100644
--- a/tests/mock/sysrepo_subscription.cpp
+++ b/tests/mock/sysrepo_subscription.cpp
@@ -23,7 +23,7 @@
 
     int operator()(
             sysrepo::S_Session sess,
-            const char *module_name,
+            [[maybe_unused]] const char *module_name,
             [[maybe_unused]] const char *xpath,
             [[maybe_unused]] sr_event_t event,
             [[maybe_unused]] uint32_t request_id)