Fix build on Travis CI [ECR-1658] (#292):

* Build the dependencies instead of using installed in the system
 to prevent illegal instructions appearing in our artefacts (the actual cause
 is still unknown).
* Disable caching of rust/target for it takes at least 2.5G, 
which is too much for Travis to archive and upload.

.travis.yml

@@ -5,12 +5,8 @@ sudo: false
 
 addons:
   apt:
-    sources:
-    - sourceline: 'ppa:chris-lea/libsodium'
     packages:
-    - libsnappy-dev
     - build-essential
-    - libsodium-dev
     - libssl-dev
     - pkg-config
 
@@ -21,12 +17,10 @@ env:
     - RUST_NIGHTLY_VERSION=nightly-2018-05-26
     - RUST_CLIPPY_VERSION=0.0.205
     - EJB_RUST_BUILD_DIR="$TRAVIS_BUILD_DIR/exonum-java-binding-core/rust/"
-    - SNAPPY_LIB_DIR=/usr/lib/x86_64-linux-gnu
 
 cache:
   directories:
     - "$HOME/.cargo"
-    - "${EJB_RUST_BUILD_DIR}/target"
     - "$HOME/.m2"
 
 before_install:
@@ -48,6 +42,10 @@ before_install:
   - cargo install --list
     # libjava_bindings.so and native application both need to load common Rust libs (eg libstd.so).
   - export LD_LIBRARY_PATH=$RUST_LIB_DIR:$LD_LIBRARY_PATH
+    # force building instead of using from apt.
+  - export SODIUM_BUILD=1
+  - export ROCKSDB_BUILD=1
+  - export SNAPPY_BUILD=1
 
 install: true  # Skip the installation step, as Maven requires
                # several extra properties when run on a CI server (see below).

exonum-java-binding-core/rust/Cargo.toml

@@ -15,7 +15,10 @@ resource-manager = []
 invocation = ["jni/invocation"]
 
 [patch.crates-io]
-exonum_sodiumoxide = { git = "https://github.com/alexander-irbis/exonum_sodiumoxide.git", branch = "exclude-1604-ECR-846" }
+# FIXME Remove with exonum 0.8+.
+exonum_rocksdb = { git = "https://github.com/alexander-irbis/exonum_rocksdb.git", branch = "fix-build" }
+# FIXME Remove with exonum 0.8+.
+exonum_sodiumoxide = { git = "https://github.com/alexander-irbis/exonum_sodiumoxide.git", branch = "fix-build-old" }
 
 [dependencies]
 # ¡Please keep README.md in sync with the Exonum version,