fix find DSO load address

DSO load address could be 0x0, so we cannot use 0x0 address
as error return.

Signed-off-by: Jovi Zhangwei <jovi.zhangwei@gmail.com>
add samples script glibc_trace.kp and glibc_sdt.kp

scripts/userspace/glibc_trace.kp: trace all functions in glibc
scripts/userspace/glibc_sdt.kp:   trace all static markers in glibc

Signed-off-by: Jovi Zhangwei <jovi.zhangwei@gmail.com>