Add some comments for zoom methods.

Also change RuntimeException to IllegalArgumentException.
bug:2458926

Change-Id: I87af31f5f3f10244131a1117bd1725c2d292b587
diff --git a/camera/ICamera.cpp b/camera/ICamera.cpp
index 724bd20..13673b5 100644
--- a/camera/ICamera.cpp
+++ b/camera/ICamera.cpp
@@ -208,7 +208,7 @@
     }
     virtual status_t sendCommand(int32_t cmd, int32_t arg1, int32_t arg2)
     {
-        LOGD("sendCommand");
+        LOGV("sendCommand");
         Parcel data, reply;
         data.writeInterfaceToken(ICamera::getInterfaceDescriptor());
         data.writeInt32(cmd);