Arrange the bybusyness logic and prevent bad busy values. #494

Job	Run time
Empty APLOGNO() test	57s
Default	5m 5s
All-static modules	4m 13s
Prefork MPM, all-modules (except cgid)	5m 33s
Worker MPM, all-modules	5m 43s
Shared MPMs, all-modules	5m 47s
Event MPM, all-modules, mod_cgid only	5m 30s
Event MPM, all-modules, no CMSG_DATA	4m 41s
Default, all-modules + install	5m 16s
Default, all-modules, random test order	6m 7s
GCC 10 maintainer-mode w/-Werror, install + VPATH	4m 51s
All-modules, APR 1.7.4, APR-util 1.6.3	5m 12s
APR 1.8.x, APR-util 1.7.x	6m 22s
Pool-debug	6m 50s
Shared MPMs (event), pool-debug, SSL/TLS variants	11m 6s
Shared MPMs (worker), pool-debug, SSL/TLS variants	10m 54s
Shared MPMs (prefork), pool-debug, SSL/TLS variants	10m 53s
litmus WebDAV tests	2m 33s
Regenerate ap_expr	5m 38s
APR 1.7.4, APR-util 1.6.3, LDAP	5m 37s
APR trunk thread debugging	5m 49s
UBSan	5m 31s
ASan	7m 33s
ASan, pool-debug	9m 44s
HTTP/2 test suite	14m 30s
MOD_TLS test suite	5m 39s
	2h 47m 34s

Provide feedback