[PowerProfiler] Make sure correct version of pySerial is imported with monsoon profiler.

[PowerProfiler] Make sure correct version of pySerial is imported with monsoon profiler.

Python 2.7.x includes pySerial version 2.5 as a distribution package. This conflicts with
our repository version of pySerial i.e. 2.7. The submodule serial.tools.* was included in
pySerial after 2.6 as per [1].

The utility function util.AddDirToPythonPath(...) appends the path at the end of the path
list. Due to this, the python interpreter picks up the pySerial library from system include
path at /usr/lib/python2.7/dist-packages/serial. This CL modifies AddDirToPythonPath(...) API to always prepend the path.

[1] http://pyserial.sourceforge.net/pyserial_api.html#module-serial.tools.list_ports

NOTRY=true

Review URL: https://codereview.chromium.org/321773002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@276531 0039d316-1c4b-4281-b951-d872f2087c98