Improve 'updateWiki' to either update the regular or the test landing page

If specified, the option '--test-wiki-update' will mean that the
landing page 'User:UpdateBot/Issue-2843-Consolidated-Extension-List'
will be used instead of 'Documentation'.
Exclude '_CPack_Packages' from module build directories search

For now let's consider only modules existing in the build directory.

An possible improvement could be to either:
 (a) consider only module existing in _CPack_Packages
 (b) differentiate both cases "build tree" vs "install tree" and report
which cases are failing.