kpatch-build: DEBUG for create-diff-object

Add -d option to create-diff-object when DEBUG is set.  That way for
weird kpatch-build issues we can just tell people to use the -d flag and
then provide the build log.
fix review comment
Merge pull request #255 from jpoimboe/kpatch-build-debug

kpatch-build: DEBUG for create-diff-object
kmod/core: don't print "patching module 'vmlinux'"
Merge pull request #256 from jpoimboe/no-print-vmlinux-module

kmod/core: don't print "patching module 'vmlinux'"
kpatch-build: --sourcedir 2.0

In my experience this is a much more useful implementation of the
"--sourcedir" option:

- use the source tree in-place rather than first copying it to
  ~/.kpatch/src.  In my case this avoids a 5GB copy, including the
  entire .git subdirectory, and allows ccache to be reused.

- find the vmlinux and .config files in the sourcedir

- autodetect the ARCHVERSION
kmod: fix uninstall path
Merge pull request #259 from jpoimboe/fix-uninstall

kmod: fix uninstall path
kpatch: remove the path to modinfo to fix the info function
Merge pull request #260 from goldyfruit/master

kpatch: remove the path to modinfo to fix the info function
fix review comment
Merge pull request #258 from jpoimboe/sourcedir-2.0

kpatch-build: --sourcedir 2.0