Let genrule have the entrance depend on signapk

Currently, it may be a good idea to let genrule module depend on
java_library_host by changing soong. To change signapk module type from
java_library_host to java_binary_host makes the genrule can depend on the
signapk module directly and generate the signapk.jar at the same time.

Test: for i in `seq 1 10` ; \
        do\
            make clean; \
            make -j64 apexer_test_host_tools; \
        done
Bug: 160632228
Bug: 157878202
Change-Id: I63ae661b9b419ddc6e69ccfc9a29fd28b116c0b5
Merged-In: I63ae661b9b419ddc6e69ccfc9a29fd28b116c0b5
(cherry picked from commit d8442b4c)