extract CppunitTest_sw_ooxmlfieldexport from CppunitTest_sw_ooxmlimport

before:
$ time make -sr CppunitTest_sw_ooxmlexport
real    4m5.728s

after:
$ time make -sr CppunitTest_sw_ooxmlexport
real    3m24.446s

and the new CppunitTest_sw_ooxmlfieldexport can run in parallel.

Change-Id: I5a1d121f51e2d09a1c2126a33484e956c5c706a8