Task-number: QTCREATORBUG-9068

This makes 'qmake' the first qmake binary to check when iterating
over possible Qt:s on the system. Without this if the system uses the
old way of adding version suffixes to Qt binaries (kept for Qt 4 for
compatibility reasons in Debian and Ubuntu), Qt 4 would be used
over Qt 5 even if Qt 5 is the default.

I've tested it to be working on Ubuntu 13.04 and 12.04 LTS as follows,
with Qt Creator 2.7 patched. At each phase I removed the old Qt Creator
configuration to simulate first run.

1. With Qt 5 as the default, no qmake-qt4, Qt 5 continues to be found.
2. With Qt 5 as the default + qmake-qt4, Qt Creator now still finds Qt 5
as it's the /usr/bin/qmake - this is the part that fixes the bug.
3. With Qt 4 as the default, Qt 4 is found via /usr/bin/qmake
(before, it would have been found via qmake-qt4 symlink).
4. With qtchooser removed but qt4-qmake still installed, Qt 4 is
found via /usr/bin/qmake-qt4 as a fallback.

Change-Id: I05ed6dc0e81336330a0b3b458249e9c7c928cc40
Reviewed-by: Daniel Teske <daniel.teske@digia.com>