Ptrace syscall testing fully support on Arm64

I plan to enable all syscall tests on Arm64.
Currently, there are several random problemes left:
* [x] udp_socket_test_runsc_ptrace_hostnet
* [x] random memory barrier issue in mmap testing
* [x] runtime fails with missing stack maps in race mode
Description: In race mode, when calling the go function in asm code, there will be an missing stack maps issue.
* [x] Since golang 1.15.2 has fixed the arm64 overflow issue, we need to update go_version into 1.15.2 in gVisor.
* [ ] A random seccomp bpf fail issue in syscall testing

Currently known golang issues:
* [x] overflow issue - need golang 1.15.2+
https://go-review.googlesource.com/c/go/+/233097

/assign @lubinszARM