Remove color logging feature from qtestlib.

Remove color logging feature from qtestlib.

This feature was undocumented and only worked if a secret environment
variable was set, the test output was going to a real console, and plain
text test results were being generated.  Including code in testlib for
fancy presentation of test results conflicts with testlib's stated goal
of being a lightweight framework where every feature contributes to
finding bugs, so this feature is being removed.  If fancy presentation
of test output is required, it should be achieved by post-processing the
test output outside of the test framework.

Change-Id: I872165c4d2c3d2498c3aa039070ecf319e237ca1
Reviewed-on: http://codereview.qt.nokia.com/3432
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Rohan McGovern <rohan.mcgovern@nokia.com>