vmm: Emulate testb imm8,r/m8

Add support for "testb imm8,r/m8" emulation.

PR: 261940
PR: 282852
Reviewed by: markj, emaste
Approved by: emaste (mentor)
Obtained from: Illumos (https://www.illumos.org/issues/14483)
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D49208