test/zdtm: use TEST_PATTERN as argument

Use TEST_PATTERN instead of TEST_NAME as argument.
All previous zdtm commands can be used still.
It is useful to run certain part of tests.

Example of running in-namespace tests only:
	./test/zdtm.sh ^ns/.*

Signed-off-by: Yicheng Qin <yichengq@google.com>
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>