Increase default Agent flush timeout

[ofek]

Motivation

Occasionally the Agent shuts down too fast for memory profiling metrics to come in

[codecov]

Codecov Report

Merging #4714 into master will decrease coverage by 21.49%.
The diff coverage is n/a.

Impacted Files	Coverage Δ
datadog_checks_dev/tests/test_docker.py	48.14% <0%> (-51.86%)	⬇️
datadog_checks_dev/datadog_checks/dev/env.py	25.71% <0%> (-31.43%)	⬇️
datadog_checks_dev/datadog_checks/dev/docker.py	31.14% <0%> (-29.51%)	⬇️
datadog_checks_dev/tests/test_conditions.py	82.25% <0%> (-17.75%)	⬇️
...atadog_checks_dev/datadog_checks/dev/subprocess.py	62.16% <0%> (-16.22%)	⬇️
...atadog_checks_dev/datadog_checks/dev/conditions.py	80.95% <0%> (-4.77%)	⬇️
datadog_checks_dev/datadog_checks/dev/_env.py	46.15% <0%> (-4.62%)	⬇️
vertica/tests/metrics.py
riakcs/datadog_checks/riakcs/riakcs.py
oracle/tests/test_oracle.py
... and 814 more