IMPALA-12434: Isolate pkg_resources.py to its own directory

In some build environments, the impala-shell Python 3
virtualenv install fails due to interactions with
shell/pkg_resources.py. This doesn't reproduce in the standard
development environment, but it is consistent. It seems to
be related to invoking a command in ${IMPALA_HOME}/shell
and the pkg_resources.py being in that directory.

To avoid any interactions, this moves shell/pkg_resources.py
to shell/legacy/pkg_resources.py. This keeps it off of the
path for the failing command, and it also keeps it off of
our PYTHONPATH (which includes ${IMPALA_HOME}/shell).

Testing:
 - Ran a build in the affected build environment
 - Ran a core job

Change-Id: Id8f2d8a8472c7bb405bf88673ed9779e23cde1d6
Reviewed-on: http://gerrit.cloudera.org:8080/20468
Reviewed-by: Michael Smith <michael.smith@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>

bin/check-python-syntax.sh

@@ -28,7 +28,7 @@ for file in $(git ls-files '**/*.py'); do
         continue
     fi
     # Skip the shell's pkg_resources.py
-    if [[ "${file}" == "shell/pkg_resources.py" ]]; then
+    if [[ "${file}" == "shell/legacy/pkg_resources.py" ]]; then
         continue
     fi
 

bin/rat_exclude_files.txt

@@ -225,7 +225,7 @@ cmake_modules/FindJNI.cmake
 
 # http://www.apache.org/legal/resolved.html#category-a : Python Software Foundation
 # License is allowed.
-shell/pkg_resources.py
+shell/legacy/pkg_resources.py
 
 # Notices in Impala as required by ASF rules:
 DISCLAIMER

shell/make_shell_tarball.sh

@@ -186,7 +186,7 @@ cp ${SHELL_HOME}/impala_shell.py ${TARBALL_ROOT}
 cp ${SHELL_HOME}/compatibility.py ${TARBALL_ROOT}
 cp ${SHELL_HOME}/thrift_printer.py ${TARBALL_ROOT}
 
-cp ${SHELL_HOME}/pkg_resources.py ${TARBALL_ROOT}/legacy
+cp ${SHELL_HOME}/legacy/pkg_resources.py ${TARBALL_ROOT}/legacy
 
 pushd ${BUILD_DIR} > /dev/null
 echo "Making tarball in ${BUILD_DIR}"