core (launcher): set AsyncIO reactor in launcher

The reactor is now set in the launcher, as it is the first script to be
loaded. This should avoid race conditions when some Twisted or libervia
packages are imported and end up importing `twisted.internet.reactor`,
which installs the default reactor before the AsyncIO one. The AsyncIO
reactor is still set in `twisted.plugin.libervia_backend_plugin` (but it
no longer fails if already set), in case the backend is started as a
plugin (although this is not recommended anyway)

twisted/plugins/libervia_backend_plugin.py

@@ -17,12 +17,14 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 
+from twisted.internet.error import ReactorAlreadyInstalledError
 from zope.interface import implementer
 from twisted.python import usage
 from twisted.plugin import IPlugin
 from twisted.application.service import IServiceMaker
 
 # XXX: We need to configure logs before any log method is used, so here is the best place.
+from libervia.backend.core import exceptions
 from libervia.backend.core.constants import Const as C
 from libervia.backend.core.i18n import _
 
@@ -33,7 +35,8 @@ install_wokkel_patches()
 
 def initialise(options):
     """Method to initialise global modules"""
-    # XXX: We need to configure logs before any log method is used, so here is the best place.
+    # XXX: We need to configure logs before any log method is used, so here is the best
+    # place.
     from libervia.backend.core import log_config
 
     log_config.libervia_configure(C.LOG_BACKEND_TWISTED, C, backend_data=options)
@@ -67,7 +70,15 @@ class LiberviaMaker:
     def makeService(self, options):
         from twisted.internet import asyncioreactor
 
-        asyncioreactor.install()
+        try:
+            asyncioreactor.install()
+        except ReactorAlreadyInstalledError as e:
+            from twisted.internet import reactor
+
+            if not isinstance(reactor, asyncioreactor.AsyncioSelectorReactor):
+                raise exceptions.InternalError(
+                    f"Wrong reactor installed: {reactor}"
+                ) from e
         self.set_debugger()
         # XXX: Libervia must be imported after log configuration,
         #      because it write stuff to logs