Switch back to using git for the agent ref

A diskimage-builder patch [1] broke our amphora-agent element by
uninstalling git prior to the post-install.d phase.
A followup patch in Octavia [2] changed how we get the git
reference to awking an git internal log file. This seems fragile
to me, so I am proposing this alternative.
This patch updates our element to finish using git before the
install.d phase is complete.

[1] https://review.opendev.org/745678
[2] https://review.opendev.org/745683

Change-Id: I9a346b626f852171ec00d2868ccb6f98b1fb8994

elements/amphora-agent/install.d/amphora-agent-source-install/75-amphora-agent-install

@@ -16,6 +16,9 @@ $AMP_VENV/bin/pip install pip --upgrade
 
 $AMP_VENV/bin/pip install -U -c /opt/upper-constraints.txt /opt/amphora-agent
 
+# Let's capture the git reference we installed in the venv
+git  --git-dir=/opt/amphora-agent/.git rev-parse HEAD >> /opt/amphora-agent.gitref
+
 # Workaround https://github.com/svinota/pyroute2/issues/724
 # TODO(johnsom) Remove once a that is resolved and 0.5.13 has been blocked in
 # global requirements.

elements/amphora-agent/post-install.d/90-remove-build-deps

@@ -9,7 +9,6 @@ set -o pipefail
 
 [ "${DIB_INSTALLTYPE_amphora_agent:-}" = "package" ] && exit 0
 
-awk 'FNR == 1 {print $1}' /opt/amphora-agent/.git/logs/HEAD >> /opt/amphora-agent.gitref
 rm -rf /opt/amphora-agent
 
 case $DISTRO_NAME in