run-tests: ensure install directories exist
As part of the transition to setuptools, it was discovered that
setuptools doesn't create install directories for you where distutils
apparently did. This was causing run-tests.py to fail when creating the
temporary hg install.
We work around this problem by creating the install directories before
running setup.py.
run-tests: avoid printing extra newlines from install log
If an installation error occurs, we print the install log. Before,
output had extra newlines because we were using "print" on data that was
already newline terminated.