Fix shadow variable warning
Fix shadow variable warning

clang 3.8.0 on FreeBSD 11.0-ALPHA4 complains that a local variable "tc"
shadows a class member coming from atf-c++.  This warning seems new and
inaccurate... but we have to workaround it with a rename.

jmmv/kyua,jmmv/kyua,jmmv/kyua,jmmv/kyua