Allow module to specify LOCAL_INSTALLED_MODULE_STEM

With this change, you can install a shared library with module name foo
as bar.so to the system.img with:
LOCAL_INSTALLED_MODULE_STEM := bar.so
Note that we in general still disallow a static/shared library to
specify LOCAL_MODULE_STEM or LOCAL_BUILT_MODULE_STEM, because the build
system uses LOCAL_MODULE to compute build time dependencies, such as
export_includes, the -l linker flag etc.
Also, if you use LOCAL_INSTALLED_MODULE_STEM to change the installed
file name and if any other module links against this library, you may
run into runtime error: the library name baked in to the binary is not
the same as file name in the system image.

Change-Id: I55b571c8139c3bda07a4a0e50cea0f20d8d6c168