Fix remote host emulator directory name

The latest emulator zip compiled for aarch64 contains two
subdirectories, emulator and _codesign. It causes _GetSubdirNameInZip to
return an invalid value. This commit defines a constant value for the
subdirectory in emulator zip.

Test: acloud-dev create -vv --avd-type goldfish \
      --branch aosp-master --build-id 8466348 \
      --build-target sdk_x86_64-sdk \
      --config-file ~/acloud-user.config \
      --service-account-json-private-key-path ~/key.json \
      --host-ssh-private-key-path ~/id_rsa \
      --host-user root --host 192.168.9.2 \
      --image-download-dir ~/download \
      --report-file report.json
Bug: 221996508
Change-Id: Iebb024676c38af665afc5c67f544e90a1ec7e264
2 files changed