PARQUET-989: [C++] Fix toolchain Travis CI failure

I mistakenly thought that the toolchain build had passed in #330, but when I added arrow-cpp it introduced failures.  I dropped the `allow_failures` to require the toolchain build to pass to see build success on GitHub. @majetideepak if you could take a look and let me know if this is OK (assuming the Travis CI build passes).

Author: Wes McKinney <wes.mckinney@twosigma.com>

Closes #331 from wesm/PARQUET-989 and squashes the following commits:

a646dcc [Wes McKinney] Remove arrow-cpp from thirdparty toolchain for now
88c6d3e [Wes McKinney] Do not permit toolchain build failure
2785ea7 [Wes McKinney] Set LD_LIBRARY_PATH, link dynamically to libarrow
diff --git a/.travis.yml b/.travis.yml
index 540cc09..b332cf1 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -37,8 +37,6 @@
     - pkg-config
 matrix:
   fast_finish: true
-  allow_failures:
-    - env: PARQUET_BUILD_GROUP=toolchain
   include:
   - compiler: gcc
     os: linux
diff --git a/ci/travis_script_toolchain.sh b/ci/travis_script_toolchain.sh
index cb0a719..db1b92b 100755
--- a/ci/travis_script_toolchain.sh
+++ b/ci/travis_script_toolchain.sh
@@ -40,7 +40,7 @@
 conda info -a
 
 conda create -y -q -p $CPP_TOOLCHAIN \
-      boost-cpp arrow-cpp zlib thrift-cpp snappy brotli cmake git \
+      boost-cpp zlib thrift-cpp snappy brotli cmake git \
       -c conda-forge
 
 # ----------------------------------------------------------------------
@@ -48,13 +48,13 @@
 : ${CPP_BUILD_DIR=$TRAVIS_BUILD_DIR/parquet-build}
 export PARQUET_TEST_DATA=$TRAVIS_BUILD_DIR/data
 export PARQUET_BUILD_TOOLCHAIN=$CPP_TOOLCHAIN
+export LD_LIBRARY_PATH=$CPP_TOOLCHAIN/lib:$LD_LIBRARY_PATH
 export BOOST_ROOT=$CPP_TOOLCHAIN
 
 cmake -DPARQUET_CXXFLAGS=-Werror \
       -DPARQUET_TEST_MEMCHECK=ON \
       -DPARQUET_ZLIB_VENDORED=off \
       -DPARQUET_ARROW=ON \
-      -DPARQUET_ARROW_LINKAGE=static \
       -DPARQUET_GENERATE_COVERAGE=1 \
       $TRAVIS_BUILD_DIR