Azure/GitLab: Ensure we use requirements.txt for testsuites

Given that test/py/requirements.txt has all required test modules, make
use of that rather than a manual pip install list before running our
assorted tool testsuites.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/.azure-pipelines.yml b/.azure-pipelines.yml
index d176e04..59e99b8 100644
--- a/.azure-pipelines.yml
+++ b/.azure-pipelines.yml
@@ -144,7 +144,7 @@
           export USER=azure
           virtualenv -p /usr/bin/python3 /tmp/venv
           . /tmp/venv/bin/activate
-          pip install pyelftools pytest pygit2
+          pip install -r test/py/requirements.txt
           export UBOOT_TRAVIS_BUILD_DIR=/tmp/sandbox_spl
           export PYTHONPATH=${UBOOT_TRAVIS_BUILD_DIR}/scripts/dtc/pylibfdt
           export PATH=${UBOOT_TRAVIS_BUILD_DIR}/scripts/dtc:${PATH}