Set Travis dist to xenial, add py3.7
Set Travis dist to xenial, add py3.7

iphoting/healthchecks,iphoting/healthchecks,healthchecks/healthchecks,healthchecks/healthchecks,healthchecks/healthchecks,iphoting/healthchecks,healthchecks/healthchecks,iphoting/healthchecks