The default expire time for a remote EC2 instance is 2 hours.

Possible changes:

• Add an optional parameter -e to buildscripts/launch_evergreen_ec2_instance.sh to add --tagExpireHours parameter to invocation of buildscripts/aws_ec2.py
• Add a macro variable, expire_hours in etc/evergreen.yml to call buildscripts/launch_evergreen_ec2_instance.sh