oe-build-perf-test: tag results committed to Git

oe-build-perf-test: tag results committed to Git

Create a Git tag when committing results to a Git repository. This patch
also implements --commit-results-tag command line option for controlling
the tag name. The value
is a format string where the following fields may be used:
- {git_branch} - target branch being tested
- {git_commit} - target commit being tested
- {tester_host} - hostname of the tester machine

Tagging can be disabled by giving an empty string to
--commit-results-tag. The option has no effect if --commit-results is
not defined.

(From OE-Core rev: 60059ff5b81d6ba9ba344161d51d1290559ac2df)

Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>