Clean stale python object files and cached directories in buildall.
Clean stale python object files and cached directories in buildall.

We can potentially leave stale object files and directories in the build directory,
causing the python imports to get confused; More importantly, this results in a stale
build environment. This patch cleans cached object files and directories.

Additionally, it makes buildall more robust by using pushd/popd instead of simply cd'ing
into a directory.

Change-Id: Ie8b20fc1844189d15d8c87ffcbd65e095cc4293e
Reviewed-on: http://gerrit.cloudera.org:8080/482
Reviewed-by: Ishaan Joshi <d1d1e60202ec9f2503deb1b724986485a125d802@cloudera.com>
Tested-by: Internal Jenkins

ibmsoe/ImpalaPPC,ibmsoe/ImpalaPPC,ibmsoe/ImpalaPPC,ibmsoe/ImpalaPPC,ibmsoe/ImpalaPPC,ibmsoe/ImpalaPPC,ibmsoe/ImpalaPPC