Various minor cleanups in the linux bionic scripts.
Test: env DIST_DIR=out/dist art/tools/dist_linux_bionic.sh -j80 \
com.android.art.host com.android.support.apexer
Test: art/tools/build_linux_bionic_tests.sh -j80
Bug: 229123823
Change-Id: I2ba87b1ef0aff38c60e351f237b59496d5b3c554