[BUGFIX] Improve Windows support for functional tests

Solve some issues running function tests on windows OS

* Disable colors, this is hardly supported in windows CLI,
  enable in .travis.yml explicitly
* Convert the web root path into a unix styled one to prevent a
  mix between backslashes and forward slashes
* Improve finding the PHP binary as the system constants PHP_BINDIR
  is defined with "C:\php" even if PHP is installed in a different folder
* Improves command line argument escaping for special windows
  requirements.

Resolves: #57524
Releases: 6.2
Change-Id: I80b1652e35b816f8ca93929950d014c45b9535d1