Support instance directory outside of acloud temporary directory

This commit adds --local-instance-dir that links the instance directory
to the specified directory. When acloud deletes and restarts the
instance, it preserves the directory. The infrastructure can safely
collect the log files in it.

Test: acloud-dev create --local-instance --local-image \
      --local-instance-dir ./temp
Bug: 160942364
Change-Id: I4097cdd4ff924df539ed2c1073663a1240472a57
9 files changed