Fix some automake warnings

Fix some automake warnings

src/Makefile.am:1286: warning: variable 'test_plugin_virt_SOURCES' is defined but no program or
src/Makefile.am:1286: library has 'test_plugin_virt' as canonical name (possible typo)
src/Makefile.am:1290: warning: variable 'test_plugin_virt_LDADD' is defined but no program or
src/Makefile.am:1290: library has 'test_plugin_virt' as canonical name (possible typo)
src/Makefile.am:1289: warning: variable 'test_plugin_virt_LDFLAGS' is defined but no program or
src/Makefile.am:1289: library has 'test_plugin_virt' as canonical name (possible typo)
autoreconf: Leaving directory `.'