truncate03: impose max file size limit for EFBIG test

Using LLONG_MAX as maximum can fail on XFS, because here the maximum
file size is 2^63-1, so this test may unexpectedly succeed.

Impose limit via setrlimit(RLIMIT_FSIZE,..) and set value used
in EFBIG test to be twice that much.

Signed-off-by: Jan Stancek <jstancek@redhat.com>
Acked-by: Cyril Hrubis <chrubis@suse.cz>