ci/android: support issuing custom commands before running Android CTS

Some Android build may require some specific setup before running
Android CTS, for example switching to a user different than 0, or
setting some properties.

Add a mechanism to issue such commands in a generic way.

The job definition will have to set the `ANDROID_CTS_PREPARE_COMMAND`
variable with the desired command to execute right before running
Android CTS.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35380>

.gitlab-ci/android-cts-runner.sh

@@ -31,6 +31,10 @@ fi
 
 INCLUDE_FILTERS="$(grep -v -E "(^#|^[[:space:]]*$)" "$INCLUDE_FILE" | sed -e 's/\s*$//g' -e 's/.*/--include-filter "\0" /g')"
 
+if [ -n "${ANDROID_CTS_PREPARE_COMMAND:-}" ]; then
+  eval "$ANDROID_CTS_PREPARE_COMMAND"
+fi
+
 set +e
 eval "/android-cts/tools/cts-tradefed" run commandAndExit cts-dev \
   $INCLUDE_FILTERS \