CircleCI: fix NCCL install

[yf225]

The $BUILD_ENVIRONMENT checks work in test.sh but not build.sh, this PR fixes the issue.

This replaces #14124.

[yf225]

@teng-li Should we fix this error in pytorch_linux_trusty_py2_7_9_build:

Nov 18 21:13:50 /var/lib/jenkins/workspace/torch/lib/c10d/ProcessGroupMPI.cpp: In destructor 'virtual c10d::ProcessGroupMPI::AsyncWork::~AsyncWork()':
Nov 18 21:13:50 /var/lib/jenkins/workspace/torch/lib/c10d/ProcessGroupMPI.cpp:154:71: error: throw will always call terminate() [-Werror=terminate]
Nov 18 21:13:50          "Attempted destruction of AsyncWork before work has completed");
Nov 18 21:13:50                                                                        ^
Nov 18 21:13:50 /var/lib/jenkins/workspace/torch/lib/c10d/ProcessGroupMPI.cpp:154:71: note: in C++11 destructors default to noexcept

[teng-li]

@yf225 this has been fixed

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