Build vendor image for emulator

BUG: 37511975

Test: lunch sdk_gphone_x86-user, make with dist option, unzip
sdk_gphone_x86-emulator-eng.xxxx.zip to system image folder, emulator
can boot

Change-Id: I330adc6da2999031d4ed2d8c4ade4667c1d0b511
Merged-In: I75b9f0de17fece3dec5ae1662400808af321bd4d
7 files changed