jenkins.impala.io pre-existing workspace

[Tim Armstrong]

Is this a known problem? My job failed because the Impala repo already
existed on the machine:

https://jenkins.impala.io/job/ubuntu-16.04-from-scratch/164/

*23:00:24* + /usr/bin/git init /home/ubuntu/Impala*23:00:24*
Reinitialized existing Git repository in /home/ubuntu/Impala/.git/
....
*23:02:18* + for ITER in '$(seq 1 10)'*23:02:18* + echo 'ATTEMPT:
1'*23:02:18* ATTEMPT: 1*23:02:18* + /usr/bin/git checkout
FETCH_HEAD*23:02:18* + cat
/home/ubuntu/Impala/tmp.3tYBn0GUga*23:02:18* 23:02:18.712300 git.c:344
              trace: built-in: git 'checkout' 'FETCH_HEAD'*23:02:18*
error: The following untracked working tree files would be overwritten
by checkout:*23:02:18*  .clang-format*23:02:18*         .clang-tidy*23:02:18*
        .gitignore*23:02:18*    CMakeLists.txt*23:02:18*        
DISCLAIMER*23:02:18*
        EXPORT_CONTROL.md*23:02:18*     LICENSE.txt*23:02:18*   
LOGS.md*23:02:18*
        NOTICE.txt*23:02:18*    README.md*23:02:18*     be/.gitignore*23:02:18*
        be/.impala.doxy*23:02:18*       be/CMakeLists.txt*23:02:18*
        be/src/benchmarks/CMakeLists.txt*23:02:18*
        be/src/benchmarks/atod-benchmark.cc*23:02:18*
        be/src/benchmarks/atof-benchmark.cc*23:02:18*
        be/src/benchmarks/atoi-benchmark.cc*23:02:18*
        be/src/benchmarks/bit-packing-benchmark.cc*23:02:18*
        be/src/benchmarks/bitmap-benchmark.cc
...