Allow Running Container as Runner Host User (#600)

- Added `runAsHostUser` to allow running the container as the same user as the host system. This fixes most permissions issues on self-hosted runners.
- Perform android sdk setup during entrypoint.sh to ensure it has root permissions if the user switches to a non-root user
- Automatically detect android sdk target version if parameters are not already provided to configure the sdk
- Generate a new uuid for machineID to ensure separate containers are unique to reduce license activation errors
- Add exponential retry strategy for Ubuntu license activations

dist/platforms/ubuntu/steps/runsteps.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+
+#
+# Run steps
+#
+source /steps/set_extra_git_configs.sh
+source /steps/set_gitcredential.sh
+source /steps/activate.sh
+
+# If we didn't activate successfully, exit with the exit code from the activation step.
+if [[ $UNITY_EXIT_CODE -ne 0 ]]; then
+  exit $UNITY_EXIT_CODE
+fi
+
+source /steps/build.sh
+source /steps/return_license.sh
+
+#
+# Instructions for debugging
+#
+
+if [[ $BUILD_EXIT_CODE -gt 0 ]]; then
+echo ""
+echo "###########################"
+echo "#         Failure         #"
+echo "###########################"
+echo ""
+echo "Please note that the exit code is not very descriptive."
+echo "Most likely it will not help you solve the issue."
+echo ""
+echo "To find the reason for failure: please search for errors in the log above and check for annotations in the summary view."
+echo ""
+fi;
+
+#
+# Exit with code from the build step.
+#
+
+# Exiting su
+exit $BUILD_EXIT_CODE