updated status bar click response

Before now users could click anywhere on the status bar to invoke shade,
this was implemented in this CL: ag/726403.
Now, However, shade should only be invoked if users click on system icons on the
right end of the status bar which has a hover state to indicate a
clickable area.

Test: atest PhoneStatusBarViewControllerTest
Flag: NA
Fixes: 299087379

Change-Id: I5f8e2940467123e3ebb60792987447db21c1d97a