ktest: Fix make_min_config to handle new assign_configs call

Commit 6071c22e "ktest: Rewrite the config-bisect to actually work"
fixed the config-bisect to work nicely but in doing so it broke
make_min_config by changing the way assign_configs works.

The assign_configs function now adds the config to the hash even if
it is disabled, but changes the hash value to be that of the
line "# CONFIG_FOO is not set". Unfortunately, the make_min_config
test only checks to see if the config is removed. It now needs to
check if the config is in the hash and not set to be disabled.

Cc: stable@vger.kernel.org # 3.17+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>