oeqa/selftest/devtool: fix _test_devtool_add_git_url

oeqa/selftest/devtool: fix _test_devtool_add_git_url

This patch is a follow-up to the bug#15466.

As a reminder, the bug was about devtool’s submodule detection
checking for HEAD when a version is being passed.

As Vincent Kriek pointed out:
the --version that is being passed to devtool is only used for
setting the PV value in the recipe. To take into account the tag,
we add --srcrev to the command:
devtool add --srcrev v3.1.0 --version v3.1.0 mbedtls git://git@github.com/ARMmbed/mbedtls.git;protocol=https

Changes to _test_devtool_add_git_url have been made to take
into account the srcrev. srcrev will be passed as an optional
parameter because the test_devtool_add_git_style1
does not need the srcrev contrary to test_devtool_add_git_style2

Fixes [YOCTO #15466]

Signed-off-by: Alexandre Truong <alexandre.truong@smile.fr>
Reported-by: Alexandre Truong <alexandre.truong@smile.fr>
Suggested-by: Vincent Kriek <vincent@coelebs.dev>
Reviewed-by: Yoann Congal <yoann.congal@smile.fr>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>