qt5webkit: do not overwrite target python

qt5webkit: do not overwrite target python

This commit fixes an issue introduced in commit
ac16793eaaabfced0312420759e3a66cdaa1ea8e. This commit creates a link
$(@D)/bin/python pointing to the host Python 2, and adds $(@D)/bin/ to
the PATH. However, the QT5WEBKIT_INSTALL_TARGET_CMDS variable copies the
contents of $(@D)/bin/ to the target filesystem, in order to install
binaries produced by the qt5webkit build. By doing this, we overwrite
the 'python' symbolic link on the target.

In order to fix this, we simply create the 'python' symbolic link used
to trick qt5webkit to use python2 on the host in the $(@D)/host-bin/
sub-directory.

Signed-off-by: Johan Derycke <johan.derycke@barco.com>
Tested-by: Yegor Yefremov <yegorslists@googlemail.com>
[Thomas: rework commit log.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>