tests: others,rpc -- Tune up header

- string.h is missed for memX helpers
 - fcntl.h should be included instead of sys

With this patch the test-c is compiled on alpine tests,
but there is a problem related to the container itself

 | protoc-c --proto_path=. --c_out=. rpc.proto
 | gcc -g -Werror -Wall -I.   -c -o test-c.o test-c.c
 | gcc -g -Werror -Wall -I.   -c -o rpc.pb-c.o rpc.pb-c.c
 | gcc   test-c.o rpc.pb-c.o  -lprotobuf-c -o test-c
 | protoc --proto_path=. --python_out=. rpc.proto
 | cp ../../../criu/criu criu
 | chmod u+s criu
 | mkdir -p build
 | chmod a+rwx build
 | sudo -g '#1000' -u '#1000' ./criu service -v4 -W build -o service.log --address criu_service.socket -d --pidfile pidfile
 | make: sudo: Command not found

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>