RFR: JDK-8234284: [dmg] Change DMG background image to TIFF

[Alexander Matveev]

Please review fix [2] for jpackage bug [1].

  - Changed background image for DMG to TIFF format, which can be used 
to embed 2x image to support HiDPI displays.

Thanks,
Alexander

[1] https://bugs.openjdk.java.net/browse/JDK-8234284

[2] http://cr.openjdk.java.net/~almatvee/8234284/webrev.00/