camerad: faster exposure convergence at startup (#36424)

* might converge faster

* accept darker at start

* accept darker at start

* it was unreasonably lax

system/camerad/cameras/camera_qcom2.cc

@@ -50,7 +50,7 @@ public:
 
   Rect ae_xywh = {};
   float measured_grey_fraction = 0;
-  float target_grey_fraction = 0.3;
+  float target_grey_fraction = 0.125;
 
   float fl_pix = 0;
   std::unique_ptr<PubMaster> pm;

system/camerad/test/test_exposure.py

@@ -20,7 +20,7 @@ class TestCamerad:
 
   def _is_exposure_okay(self, i, med_mean=None):
     if med_mean is None:
-      med_mean = np.array([[0.2,0.4],[0.2,0.6]])
+      med_mean = np.array([[0.18,0.3],[0.18,0.3]])
     h, w = i.shape[:2]
     i = i[h//10:9*h//10,w//10:9*w//10]
     med_ex, mean_ex = med_mean