Setup Indy SDK build environment for Ubuntu based distro (Ubuntu 16.04)

Install Rust and rustup (https://www.rust-lang.org/install.html).

Install required native libraries and utilities:

apt-get update && \
apt-get install -y \
   build-essential \
   pkg-config \
   cmake \
   libssl-dev \
   libsqlite3-dev \
   libsodium-dev

Checkout and build the library:

git clone https://github.com/hyperledger/indy-sdk.git
cd ./indy-sdk/libindy
cargo build
cd ..

Run integration tests:
- Start local nodes pool on 127.0.0.1:9701-9708 with Docker:
```
docker build -f ci/indy-pool.dockerfile -t indy_pool .
docker run -itd -p 9701-9708:9701-9708 indy_pool
```
  In some environments, this approach with mapping of local ports to container ports can't be applied. Dockerfile ci/indy-pool.dockerfile supports optional pool_ip param that allows changing ip of pool nodes in generated pool configuration. The following commands allow to start local nodes pool in custom docker network and access this pool by custom ip in docker network:
```
docker network create --subnet 10.0.0.0/8 indy_pool_network
docker build --build-arg pool_ip=10.0.0.2 -f ci/indy-pool.dockerfile -t indy_pool .
docker run -d --ip="10.0.0.2" --net=indy_pool_network indy_pool
```
  If you use this method then you have to specify the TEST_POOL_IP as specified below when running the tests.
  
  It can be useful if we want to launch integration tests inside another container attached to the same docker network.
- Run tests
```
cd libindy
RUST_TEST_THREADS=1 cargo test
```
  It is possible to change ip of test pool by providing of TEST_POOL_IP environment variable:
```
RUST_TEST_THREADS=1 TEST_POOL_IP=10.0.0.2 cargo test
```

See libindy/ci/ubuntu.dockerfile for example of Ubuntu based environment creation in Docker.