qt5-native, qtjsbackend-native: fix .pri and .prl pointing to WORKDIR or absolute sysroot

* fix paralel build
* default make does good job, cleans mkspecs, installs all headers and
  libs needed for qtjsbackend-native
* only variables referencing WORKDIR are now QMAKE_PRL_BUILD_DIR
  ./x86_64-linux/usr/lib/libQt5Network.prl:QMAKE_PRL_BUILD_DIR = /OE/oe-core/tmp-eglibc/work/x86_64-linux/qt5-native/5.0.1-r0.0/qtbase-opensource-src-5.0.1/src/network/
  ./x86_64-linux/usr/lib/libQt5Xml.prl:QMAKE_PRL_BUILD_DIR = /OE/oe-core/tmp-eglibc/work/x86_64-linux/qt5-native/5.0.1-r0.0/qtbase-opensource-src-5.0.1/src/xml/
  ./x86_64-linux/usr/lib/libQt5Bootstrap.prl:QMAKE_PRL_BUILD_DIR = /OE/oe-core/tmp-eglibc/work/x86_64-linux/qt5-native/5.0.1-r0.0/qtbase-opensource-src-5.0.1/src/tools/bootstrap/
  ./x86_64-linux/usr/lib/libQt5Concurrent.prl:QMAKE_PRL_BUILD_DIR = /OE/oe-core/tmp-eglibc/work/x86_64-linux/qt5-native/5.0.1-r0.0/qtbase-opensource-src-5.0.1/src/concurrent/
  ./x86_64-linux/usr/lib/libQt5Core.prl:QMAKE_PRL_BUILD_DIR = /OE/oe-core/tmp-eglibc/work/x86_64-linux/qt5-native/5.0.1-r0.0/qtbase-opensource-src-5.0.1/src/corelib/
  ./x86_64-linux/usr/lib/libQt5Test.prl:QMAKE_PRL_BUILD_DIR = /OE/oe-core/tmp-eglibc/work/x86_64-linux/qt5-native/5.0.1-r0.0/qtbase-opensource-src-5.0.1/src/testlib/
  ./x86_64-linux/usr/lib/libQt5Sql.prl:QMAKE_PRL_BUILD_DIR = /OE/oe-core/tmp-eglibc/work/x86_64-linux/qt5-native/5.0.1-r0.0/qtbase-opensource-src-5.0.1/src/sql/
  ./x86_64-linux/usr/lib/libQt5DBus.prl:QMAKE_PRL_BUILD_DIR = /OE/oe-core/tmp-eglibc/work/x86_64-linux/qt5-native/5.0.1-r0.0/qtbase-opensource-src-5.0.1/src/dbus/

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
qt5-native: rename to qtbase-native to avoid confusion

* we also had PROVIDES for qt5-tools-native, this makes it a bit easier to see what is what

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
qtbase: don't touch STAGING and bypass sstate

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