build and install core module with make

Build and install the kpatch core module with make and make install,
rather than building it every time with kpatch build.

The only downside to this approach is that the user has to make and make
install kpatch every time they get a new kernel.  But this is only
temporary, until the kpatch module is delivered in an RPM.
Merge pull request #14 from jpoimboe/core-module

build and install core module with make