Re-enable Linux build on Jenkins #4116
Description
Recently the build of xamarin-android on Linux seems to be working again, at least for certain flavors. While Ubuntu 16.04 currently fails, I was able to perform a successful build on 18.04, generating a tarball xamarin.android-oss-v10.2.99.129_Linux-x86_64_master_7674dad7-Debug.tar.bz2.
The Jenkins build on Linux at https://jenkins.mono-project.com/view/Xamarin.Android/job/xamarin-android-linux/ seems to be disabled since July 31, 2019, and was failing since Apr 17, 2019, see https://jenkins.mono-project.com/view/Xamarin.Android/job/xamarin-android-linux/lastSuccessfulBuild/ (version 9.2.99.172).
It would be great if the build could be enabled again. There are a number of tutorials on the web for using xamarin-android on Linux, all of which refer to the old version mentioned above.