fix: Cleanup logs when Firebase RTDB does no exist (#76)

The emitted logs when the DB does not exist will now resemble:

```
I0221 20:25:54.661298 93984 firebase_client.py:402] Failed to check debuggee presence at cdbg/debuggees/d-93910f74/registrationTimeUnixMsec: NotFoundError('404 Not Found')
I0221 20:25:54.661362 93984 firebase_client.py:373] registering at https://my-project-cdbg.firebaseio.com, path: cdbg/debuggees/d-93910f74
I0221 20:25:54.690697 93984 firebase_client.py:390] Failed to register debuggee: NotFoundError('404 Not Found')
```

src/googleclouddebugger/firebase_client.py

@@ -382,10 +382,10 @@ def _RegisterDebuggee(self):
 
       self.register_backoff.Succeeded()
       return (False, 0)  # Proceed immediately to subscribing to breakpoints.
-    except BaseException:
+    except BaseException as e:
       # There is no significant benefit to handing different exceptions
       # in different ways; we will log and retry regardless.
-      native.LogInfo(f'Failed to register debuggee: {traceback.format_exc()}')
+      native.LogInfo(f'Failed to register debuggee: {repr(e)}')
       return (True, self.register_backoff.Failed())
 
   def _CheckDebuggeePresence(self):
@@ -394,9 +394,8 @@ def _CheckDebuggeePresence(self):
       snapshot = firebase_admin.db.reference(path).get()
       # The value doesn't matter; just return true if there's any value.
       return snapshot is not None
-    except BaseException:
-      native.LogInfo(
-          f'Failed to check debuggee presence: {traceback.format_exc()}')
+    except BaseException as e:
+      native.LogInfo(f'Failed to check debuggee presence at {path}: {repr(e)}')
       return False
 
   def _MarkDebuggeeActive(self):