qmake/property: rename QT_INSTALL_CONFIGURATION to QT_INSTALL_SETTINGS

* this variable is referenced from configure and configureapp.cpp as QT_INSTALL_SETTINGS
  property.cpp was only place using name QT_INSTALL_CONFIGURATION

Change-Id: I3ba40d5f8773fe9aea728c5b2418aa55cecc92da
qt_module: Fix paths in .prl files

* qmake does not prefix them with QT_SYSROOT when using them
  so e.g. when building qtdeclarative we get -L/usr/lib to LINKAGE
  variable, which is unsafe for cross-compilation
* writting QT_SYSROOT in .prl files is dangerous for sstate when
  builds are in different directories, so we need
  SSTATE_SCAN_FILES += "*.pri *.prl"
  to make them relocateble

Change-Id: I4b66dcad539a3ba876d8e4ee2eb2ccd626cd03ea
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>