scheduled-backup: segmentation fault when backup user's password is empty

[LinuxGit]

Bug Report

What version of Kubernetes are you using?

v1.12.2

What version of TiDB Operator are you using?

TiDB Operator Version: version.Info{TiDBVersion:"2.1.0", GitVersion:"v1.0.0-beta.2.38+758c9888ea4245-dirty", GitCommit:"758c9888ea4245f4d651f8f3f95c31290131f2e4", GitTreeState:"dirty", BuildDate:"2019-06-03T11:39:25Z", GoVersion:"go1.12.5", Compiler:"gc", Platform:"linux/amd64"}

What storage classes exist in the Kubernetes cluster and what are used for PD/TiKV pods?

rook-ceph-block

What's the status of the TiDB cluster pods?

$ kubectl get po -n l9bf43f600323e55
NAME READY STATUS RESTARTS AGE
l9bf43f600323e55-discovery-858d4d4dcb-wxzmh 1/1 Running 0 56m
l9bf43f600323e55-monitor-7d45499bc9-5cj7j 2/2 Running 0 56m
l9bf43f600323e55-pd-0 1/1 Running 0 54m
l9bf43f600323e55-pd-1 1/1 Running 1 56m
l9bf43f600323e55-pd-2 1/1 Running 0 56m
l9bf43f600323e55-scheduled-backup-1562643000-dv6hv 0/1 CrashLoopBackOff 5 5m5s
l9bf43f600323e55-tidb-0 3/3 Running 0 52m
l9bf43f600323e55-tidb-initializer-hbbj4 0/1 Completed 6 56m
l9bf43f600323e55-tikv-0 1/1 Running 0 53m
l9bf43f600323e55-tikv-1 1/1 Running 0 53m
l9bf43f600323e55-tikv-2 1/1 Running 0 53m

What did you do?

enable scheduledBackup

What did you expect to see?
scheduled-backup pod's status is Completed.

What did you see instead?
scheduled-backup pod's status is CrashLoopBackOff.
refer: #634 (comment)

If password in backup-secret is empty, setting gc_life_time operation will segmentation fault. We need to handle this situation in _start_scheduled_backup.sh.tpl.
Remove -p flag when password is empty.