osbuild: auto-generate socket addresses for APIs

Rely on the ability of `BaseAPI` to auto-generate socket addresses
when no one was provided. The `BuildRoot` does not rely on the
sockets being created in the `BuildRoot.api` directory anymore and
will instead bind-mount each individual socket address to the well
known location via the `BaseAPI.endpoint` identifier.
Convert all API providers to take the `socket_address` as an
optional keyword argument.

test/mod/test_monitor.py

@@ -74,7 +74,7 @@ class TestMonitor(unittest.TestCase):
             logfile = os.path.join(tmpdir, "log.txt")
 
             with open(logfile, "w") as log, \
-                 API(path, args, LogMonitor(log.fileno())) as api:
+                 API(args, LogMonitor(log.fileno()), socket_address=path) as api:
                 p = mp.Process(target=echo, args=(path, ))
                 p.start()
                 p.join()