qt4: Fix sundry erroneous assumptions about ${prefix}

qt4: Fix sundry erroneous assumptions about ${prefix}

FILES_${QT_BASE_NAME}-tests was hard-coded to "/usr/tests/..." but Qt
actually installs these files into ${prefix}/tests.

Conversely, FILES_${PN}-dbg in qt4.inc was defined in terms of
${exec_prefix}/src, which appears commendable but doesn't actually match
where package.bbclass will put the sources since the latter is
hard-coded to /usr/src.

This fixes a large number of "installed but not shipped" warnings
when ${prefix} is set to something other than /usr.

(From OE-Core rev: c0cfd4f84c8f4843027332cfd6cf99c452c50dbb)

Signed-off-by: Phil Blundell <philb@gnu.org>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>