Change the base directory of remote host cuttlefish

This commit moves cuttlefish images and tools on a remote host from the
SSH users' HOME to subdirectories. Each instance with different
base-instance-num has an isolated subdirectory. Thus one SSH user
account can create multiple cuttlefish.

`acloud delete --host` does not take base-instance-num as an argument.
The command always deletes the instance with base-instance-num=1. The
other instances can only be deleted by `acloud delete --instance-names`.

Test: acloud-dev create --avd-type cuttlefish \
      --local-image ~/img --local-kernel-image ~/img \
      --cvd-host-package ~/cvd-host_package.tar.gz \
      --report-file ~/report.json -vv \
      --host-ssh-private-key-path ~/id_rsa --host 192.168.9.2 \
      --base-instance-num 7
Test: acloud-dev create --avd-type cuttlefish \
      --branch aosp-master --build-id 8883970 \
      --build-target aosp_cf_x86_64_phone-userdebug \
      --report-file ~/report.json -vv \
      --host-ssh-private-key-path ~/id_rsa --host 192.168.9.2 \
      --base-instance-num 7
Test: acloud-dev delete --host-ssh-private-key-path ~/id_rsa \
      --instance-names \
      host-192.168.9.2-7-userbuild-aosp_cf_x86_64_phone
Bug: 229812494
Change-Id: I4a7febeabf058c942f8a18d2d512d8b60eb524ec
5 files changed