Previously the maximum amount of time Vagrant would poll for whether a
machine has successfully reboot was hard coded to 120 seconds. This
change introduces the VAGRANT_MAX_REBOOT_RETRY_TIMEOUT environment
variable to allow this attribute to be configurable.
Add RSpec tests of the maximum retry logic. Since the maximum retries
are configured as a constant, we'd need to reload the class and that's
fairly ugly to do in RSpec.
Fixes#11695
a2f5d615a0