lib/oe/patch: commit with a dummy user/email when PATCHTOOL=git

lib/oe/patch: commit with a dummy user/email when PATCHTOOL=git

When using PATCHTOOL = "git", the user of the system is not really the
committer - it's the build system itself. Thus, specify "dummy" values
for username and email instead of using the user's configured values.
Various parts of the devtool code that need to make commits have also
been updated to use the same logic.

This allows PATCHTOOL = "git" and devtool to be used on systems where
git user.name / user.email has not been set (on versions of git where
it doesn't default a value under this circumstance).

If you want to return to the old behaviour where the externally
configured user name / email are used, set the following in your
local.conf:

PATCH_GIT_USER_NAME = ""
PATCH_GIT_USER_EMAIL = ""

Fixes [YOCTO #8703].

(From OE-Core rev: 765a9017eaf77ea3204fb10afb8181629680bd82)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>