Remove the black bar when in VIDEO_LAYOUT_SCALE mode.

Fixes the black bar for videoview when scaling the video uniformly to full screen mode.

The black bar appears because the DisplayMetrics doesn't return the real device screen height (it minuses the height of the status bar), then we get the wrong aspect ratio of the screen, consequently causes the black bar.

In this pull request I get the real screen resolution via the new getRealMetrics API introduced in API17.  For old devices I tried the reflection method to get the real resolution first and failover to the incorrect resolution which is the value returns by your original method.