How to get from Android Emulator to Docker Machine's container?
Ok I found two solutions:
VirtualBox port forwarding
https://stackoverflow.com/a/36458215/5076865 - After that you can access the docker app via 10.0.2.2:<your_port>
VirtualBox bridged adapter
Open docker-machine setting in VirtualBox and enable the 3rd network adapter and set it to the bridge mode. You should be able to access the docker app via 192.168.99.100:<your_port> directly from emulator.
For me the second solution is better, because I have <your_port> free on my docker host.