Option to create snapshots after first boot

[simonschiller]

In order to make Swarmer faster, it would be great if there was an option for creating snapshots on the initial boot. Maybe with an option like --create-snapshots. The idea is to create a snapshot on the initial boot because the state is clean and then start emulators with -no-snapshot-save so that we never override this clean snapshot. Snapshots should only be created if there is no existing snapshot.

You can manually create a snapshot from an emulator using these commands:

telnet 127.0.0.1 EMULATOR_PORT
auth AUTH_TOKEN // Content of $HOME/.emulator_console_auth_token
avd snapshot save default_boot
quit

This change only makes sense if avds are kept and not recreated (see #41 and #42).

[yunikkk]

Sounds good to me. Snapshot management is developing pretty actively, new 28.0.0 emulator even allows multiple snapshot instances at the same time.