Support to customize emulator build target for remote goldfish instance

Emulator build target can't stick in one fixed target name. Acloud
provide one flexible argument for user to control the emulator build
target.

Bug: 236098663
Test: acloud-dev create --avd-type goldfish --build-id 7008279 --build-target \
sdk_gphone_x86_64-userdebug --branch git_master --emulator-build-target sdk_tools_linux

Change-Id: I4d95d415986802c819218e10231ca272390de9f4
5 files changed