DRY-up logging and metrics for sending SMS

This avoids duplicating it as we add a new provider and means we
can test it all in one place (although it wasn't tested before).

I'm not sure why the previous code did "super(..)__init__" in a
non-init function - it's a bit late! - so I've just replaced it
with a call to the new "init_app" function in the parent class.

app/clients/sms/__init__.py

@@ -1,3 +1,5 @@
+from time import monotonic
+
 from app.clients import Client, ClientException
 
 
@@ -18,6 +20,10 @@ class SmsClient(Client):
     Base Sms client for sending smss.
     '''
 
+    def init_app(self, current_app, statsd_client):
+        self.current_app = current_app
+        self.statsd_client = statsd_client
+
     def record_outcome(self, success):
         log_message = "Provider request for {} {}".format(
             self.name,
@@ -31,7 +37,23 @@ class SmsClient(Client):
             self.statsd_client.incr(f"clients.{self.name}.error")
             self.current_app.logger.warning(log_message)
 
-    def send_sms(self, *args, **kwargs):
+    def send_sms(self, to, content, reference, international, sender=None):
+        start_time = monotonic()
+
+        try:
+            response = self.try_send_sms(to, content, reference, international, sender)
+            self.record_outcome(True)
+        except SmsClientResponseException as e:
+            self.record_outcome(False)
+            raise e
+        finally:
+            elapsed_time = monotonic() - start_time
+            self.statsd_client.timing(f"clients.{self.name}.request-time", elapsed_time)
+            self.current_app.logger.info("Reach request for {} finished in {}".format(reference, elapsed_time))
+
+        return response
+
+    def try_send_sms(self, *args, **kwargs):
         raise NotImplementedError('TODO Need to implement.')
 
     @property