[MXNET-908] Speed up travis builds to avoid timeouts

This PR removes some redundant build tasks and removes some slow tests
to try and decrease the number of TravisCI timeouts that would otherwise
occur on large PRs.

.travis.yml

@@ -2,7 +2,12 @@ sudo: true
 
 language: cpp
 
-cache: ccache
+cache:
+  directories:
+    - $HOME/.ccache
+    - $HOME/.cache/pip
+    - $HOME/.mxnet
+    - $HOME/Library/Caches/Homebrew
 
 os:
   - osx
@@ -17,7 +22,7 @@ before_install:
   - export PYTHONPATH=${PYTHONPATH}:${PWD}/python
 
 install:
-  - brew install ccache
+  - HOMEBREW_NO_AUTO_UPDATE=1 brew install ccache
   - export PATH="/usr/local/opt/ccache/libexec:$PATH"
   - source ci/travis/install.sh
 
@@ -29,4 +34,4 @@ script:
   - export MXNET_STORAGE_FALLBACK_LOG_VERBOSE=0
   - mv make/osx.mk config.mk
   - make -j 2
-  - python -m nose --verbose tests/python/unittest/
+  - python -m nose --with-timer --timer-top-n 20 --exclude-test=test_sparse_operator.test_elemwise_binary_ops --exclude-test=test_gluon_model_zoo.test_models --exclude-test=test_random.test_shuffle --exclude-test=test_operator.test_broadcast_binary_op --exclude-test=test_operator.test_pick --exclude-test=test_profiler.test_continuous_profile_and_instant_marker --exclude-test=test_metric_perf.test_metric_performance --exclude-test=test_operator.test_order --verbose tests/python/unittest/

ci/travis/install.sh

@@ -17,14 +17,10 @@
 # specific language governing permissions and limitations
 # under the License.
 
+# Disable brew auto-update to avoid long running updates while running tests in CI.
+export HOMEBREW_NO_AUTO_UPDATE=1
+
 if [ ${TRAVIS_OS_NAME} == "osx" ]; then
-    brew update
     brew install opencv
-    brew install python3
-    brew install fftw
-    brew install libpng
-    brew install ImageMagick
-    brew install swig
-    python -m pip install --user nose numpy cython scipy requests mock
-    python3 -m pip install --user nose numpy cython scipy requests mock
+    python -m pip install --user nose numpy cython scipy requests mock nose-timer nose-exclude
 fi