Reinstate log rollover limit

[chynesNR]

When the Agent's internal logger was log4net, there was a max of 4 rollover files retained. When this limit was removed in #1878, it impacted some customers, who rely on the strict limit to manage their storage. This will eventually be configurable (see #1880) but a temporary limit should be put in place now.

Suggested T-Shirt size (S, M, L, XL, Unknown):
S

[workato-integration]

https://issues.newrelic.com/browse/NR-163019