uwrap: Extend support for set/getgroups libc functions and syscalls.

Support reflection of groups to main process and add more thread
support.

TESTS:
	Added new test test_sync_setgroups which cover changes in code.
	This test is almost same as test_sync_setgid but is aimed to setgroups
	functions.

Signed-off-by: Robin Hack <hack.robin@gmail.com>
TESTS: Fix test_uwrap_getgroups.

This test doesn't run on machines where is more than one supplementary
group.

Signed-off-by: Robin Hack <hack.robin@gmail.com>