cmake: let vstart depend on radosgwd

cmake: let vstart depend on radosgwd

in f528f173, in cmake, the target of executable "radosgw" is renamed
to "radosgwd",  and the static library of "radosgw_a" was renamed to
"radosgw". this broke the tests which expected radosgw to be available
if "tests" was built.

in this change, both "vstart" and "tests" now depend on "radosgwd"
instead of "radosgw".

Signed-off-by: Kefu Chai <kchai@redhat.com>