Misbehavior has been observed with TSC under VirtualBox, where threads
doing small sleeps (~1 second) may miss their wake up and hang around
in a sleep state indefinitely.  Switching back to ACPI-fast decidedly
fixes it, so stop using TSC on VirtualBox at least for the time being.

This partially reverts 84eaf2cc, applying it only to VirtualBox and
increasing the quality to 0. Negative qualities can never be chosen and
cannot be chosen with the tunable recently added. If we do not have a
timecounter with a higher quality than 0, then TSC does at least leave
the system mostly usable.

PR:		253087
Reviewed by:	emaste, kib
MFC after:	3 days
Differential Revision:	https://reviews.freebsd.org/D29132