Device management fx subcommands

CommandDescription
cpcopy a file to/from a target device
flashflash and, optionally, pave a connected device
node-namesfind other names for the same node
rebootreboot a target fuchsia system
scpinvoke scp with the build ssh config
serialattach to a serial console
sftpinvoke sftp with the build ssh config
shellstart a remote interactive shell in the target device
sshinvoke ssh with the keys from $FUCHSIA_BUILD_DIR/ssh-keys
waitwait for a shell to become available
screenshottakes a screenshot and copies it to the host